diff --git a/server/src/external/stripe/subscriptions/utils/classifyStripeSubscriptionUtils.ts b/server/src/external/stripe/subscriptions/utils/classifyStripeSubscriptionUtils.ts
index ad75519ca..2652760b9 100644
--- a/server/src/external/stripe/subscriptions/utils/classifyStripeSubscriptionUtils.ts
+++ b/server/src/external/stripe/subscriptions/utils/classifyStripeSubscriptionUtils.ts
@@ -7,7 +7,7 @@ export const isStripeSubscriptionTrialing = (
 	return stripeSubscription.status === "trialing";
 };
 
-export const isStripeSubscriptionCancelling = (
+export const isStripeSubscriptionCanceling = (
 	stripeSubscription?: Stripe.Subscription,
 ) => {
 	if (!stripeSubscription) {
diff --git a/server/src/internal/billing/billingRouter.ts b/server/src/internal/billing/billingRouter.ts
index a89cbcfb5..afbe6a544 100644
--- a/server/src/internal/billing/billingRouter.ts
+++ b/server/src/internal/billing/billingRouter.ts
@@ -1,4 +1,5 @@
 import { Hono } from "hono";
+import { handleSubscriptionUpdatePreview } from "@/internal/billing/v2/subscriptionUpdate/handleSubscriptionUpdatePreview.js";
 import type { HonoEnv } from "../../honoUtils/HonoEnv.js";
 import { handleAttach } from "./attach/handleAttach.js";
 import { handleCheckoutV2 } from "./checkout/handleCheckoutV2.js";
@@ -14,3 +15,7 @@ billingRouter.post("/attach", ...handleAttach);
 billingRouter.post("/attach_v2", ...handleAttachV2);
 
 billingRouter.post("/subscriptions/update", ...handleApiSubscriptionUpdate);
+billingRouter.post(
+	"/subscriptions/preview/update",
+	...handleSubscriptionUpdatePreview,
+);
diff --git a/server/src/internal/billing/v2/billingPlan.ts b/server/src/internal/billing/v2/billingPlan.ts
index 3d42b473d..f9d7e587f 100644
--- a/server/src/internal/billing/v2/billingPlan.ts
+++ b/server/src/internal/billing/v2/billingPlan.ts
@@ -30,12 +30,19 @@ export const StripeSubscriptionActionSchema = z.discriminatedUnion("type", [
 	}),
 ]);
 
+export const StripeInvoiceActionSchema = z.object({
+	addLineParams: z.custom<import("stripe").Stripe.InvoiceAddLinesParams>(),
+});
+
+export type StripeInvoiceAction = z.infer<typeof StripeInvoiceActionSchema>;
+
 export type StripeSubscriptionAction = z.infer<
 	typeof StripeSubscriptionActionSchema
 >;
 
 export const StripeBillingPlanSchema = z.object({
-	subscription: StripeSubscriptionActionSchema.optional(),
+	subscriptionAction: StripeSubscriptionActionSchema.optional(),
+	invoiceAction: StripeInvoiceActionSchema.optional(),
 });
 
 export const AutumnBillingPlanSchema = z.object({
@@ -51,16 +58,6 @@ export const AutumnBillingPlanSchema = z.object({
 	customPrices: z.array(PriceSchema), // Custom prices to insert
 	customEntitlements: z.array(EntitlementSchema), // Custom entitlements to insert
 	customFreeTrial: FreeTrialSchema.optional(), // Custom free trial to insert
-
-	// expireCusProducts: z.array(z.string()),
-
-	// updateCusProduct: z.object({
-	// 	cusProductId: z.string(),
-	// 	options: z.array(FeatureOptionsSchema),
-	// }),
-	// entitlementChanges: z.array(
-	// 	z.object({ cusEntId: z.string(), delta: z.number() }),
-	// ),
 });
 
 export const BillingPlanSchema = z.object({
diff --git a/server/src/internal/billing/v2/compute/computeStripeUtils/buildStripeInvoiceAction.ts b/server/src/internal/billing/v2/compute/computeStripeUtils/buildStripeInvoiceAction.ts
index 376165329..64624928d 100644
--- a/server/src/internal/billing/v2/compute/computeStripeUtils/buildStripeInvoiceAction.ts
+++ b/server/src/internal/billing/v2/compute/computeStripeUtils/buildStripeInvoiceAction.ts
@@ -7,7 +7,7 @@ import {
 import type { AttachContext, StripeSubAction } from "../../typesOld";
 import { applyStripeDiscountsToLineItems } from "../../utils/stripeAdapter/applyStripeDiscounts/applyStripeDiscountsToLineItems";
 import { subToDiscounts } from "../../utils/stripeAdapter/applyStripeDiscounts/subToDiscounts";
-import { lineItemsToStripeLines } from "../../utils/stripeAdapter/stripeInvoiceOps/lineItemsToStripeLines";
+import { lineItemsToStripeLines } from "../../utils/stripeAdapter/invoiceLines/lineItemsToStripeLines";
 
 export const buildStripeInvoiceAction = ({
 	attachContext,
diff --git a/server/src/internal/billing/v2/execute/executeStripeInvoiceAction.ts b/server/src/internal/billing/v2/execute/executeStripeInvoiceAction.ts
index 6dfff0535..e9bc0d9d4 100644
--- a/server/src/internal/billing/v2/execute/executeStripeInvoiceAction.ts
+++ b/server/src/internal/billing/v2/execute/executeStripeInvoiceAction.ts
@@ -1,54 +1,31 @@
+import type { BillingContext } from "@/internal/billing/v2/billingContext";
 import { createStripeCli } from "../../../../external/connect/createStripeCli";
 import type { AutumnContext } from "../../../../honoUtils/HonoEnv";
+import type { StripeInvoiceAction } from "../billingPlan";
 import { createAndPayInvoice } from "../utils/stripeAdapter/stripeInvoiceOps/createAndPayInvoice";
-import type {
-	AttachContext,
-	StripeCheckoutAction,
-	StripeInvoiceAction,
-} from "../typesOld";
-import { executeStripeCheckoutAction } from "./executeStripeCheckoutAction";
 
 export const executeStripeInvoiceAction = async ({
 	ctx,
-	attachContext,
-	stripeCheckoutAction,
+	billingContext,
 	stripeInvoiceAction,
 }: {
 	ctx: AutumnContext;
-	attachContext: AttachContext;
-	stripeCheckoutAction: StripeCheckoutAction;
+	billingContext: BillingContext;
 	stripeInvoiceAction: StripeInvoiceAction;
 }) => {
-	const { org, env, logger } = ctx;
-	const { items, onPaymentFailure } = stripeInvoiceAction;
+	const { org, env } = ctx;
+	const { addLineParams } = stripeInvoiceAction;
 
 	const stripeCli = createStripeCli({ org, env });
 
 	// 1. Create and pay invoice
-	const { invoice, paid, error, createCheckoutSession, hostedUrl } =
-		await createAndPayInvoice({
-			stripeCli,
-			stripeCusId: attachContext.stripeCus.id,
-			stripeLineItems: items,
-			paymentMethod: attachContext.paymentMethod,
-			onPaymentFailure: onPaymentFailure,
-		});
+	const result = await createAndPayInvoice({
+		stripeCli,
+		stripeCusId: billingContext.stripeCustomer?.id,
+		stripeLineItems: addLineParams.lines,
+		paymentMethod: billingContext.paymentMethod,
+		onPaymentFailure: "return_url",
+	});
 
-	if (!paid) {
-		// 1. Either return checkout session, hosted url, or throw error
-		if (createCheckoutSession) {
-			return await executeStripeCheckoutAction({
-				ctx,
-				stripeCheckoutAction: stripeCheckoutAction,
-			});
-		}
-
-		if (hostedUrl) {
-			return hostedUrl;
-		}
-
-		throw error;
-	}
-
-	return invoice;
+	return result;
 };
diff --git a/server/src/internal/billing/v2/fetch/fetchAutumnUtils/resolveAttachActions/getUncancelAttachActions.ts b/server/src/internal/billing/v2/fetch/fetchAutumnUtils/resolveAttachActions/getUncancelAttachActions.ts
index b4a4fc461..3cb8d9f55 100644
--- a/server/src/internal/billing/v2/fetch/fetchAutumnUtils/resolveAttachActions/getUncancelAttachActions.ts
+++ b/server/src/internal/billing/v2/fetch/fetchAutumnUtils/resolveAttachActions/getUncancelAttachActions.ts
@@ -3,7 +3,7 @@ import {
 	type CusProductActions,
 	getOngoingCusProductById,
 	getScheduledMainCusProductByGroup,
-	isCusProductCanceled,
+	isCustomerProductCanceled,
 } from "@autumn/shared";
 
 /**
@@ -27,7 +27,7 @@ export const getUncancelAttachActions = ({
 
 	if (
 		!ongoingSameCusProduct ||
-		!isCusProductCanceled({ cusProduct: ongoingSameCusProduct })
+		!isCustomerProductCanceled(ongoingSameCusProduct)
 	) {
 		return undefined;
 	}
diff --git a/server/src/internal/billing/v2/handlers/handleApiSubscriptionUpdate.ts b/server/src/internal/billing/v2/handlers/handleApiSubscriptionUpdate.ts
index 27e3b7f01..d60287b46 100644
--- a/server/src/internal/billing/v2/handlers/handleApiSubscriptionUpdate.ts
+++ b/server/src/internal/billing/v2/handlers/handleApiSubscriptionUpdate.ts
@@ -14,7 +14,7 @@ export const handleApiSubscriptionUpdate = createRoute({
 			params: body,
 		});
 
-		const subscriptionUpdatePlan = computeSubscriptionUpdatePlan({
+		const subscriptionUpdatePlan = await computeSubscriptionUpdatePlan({
 			ctx,
 			updateSubscriptionContext,
 			params: body,
diff --git a/server/src/internal/billing/v2/subscriptionUpdate/compute/buildQuantityUpdateLineItems.ts b/server/src/internal/billing/v2/subscriptionUpdate/compute/buildQuantityUpdateLineItems.ts
new file mode 100644
index 000000000..83a024269
--- /dev/null
+++ b/server/src/internal/billing/v2/subscriptionUpdate/compute/buildQuantityUpdateLineItems.ts
@@ -0,0 +1,88 @@
+import {
+	type BillingPeriod,
+	cusEntToCusPrice,
+	cusProductToCusEnts,
+	type Feature,
+	type FullCusProduct,
+	findPrepaidCustomerEntitlement,
+	InternalError,
+	type LineItemContext,
+	orgToCurrency,
+	usagePriceToLineItem,
+} from "@autumn/shared";
+import { Decimal } from "decimal.js";
+import type { AutumnContext } from "@/honoUtils/HonoEnv";
+
+export const buildQuantityUpdateLineItems = ({
+	ctx,
+	customerProduct,
+	feature,
+	billingPeriod,
+	quantityDifferenceForEntitlements,
+	currentEpochMs,
+}: {
+	ctx: AutumnContext;
+	customerProduct: FullCusProduct;
+	feature: Feature;
+	billingPeriod?: BillingPeriod;
+	quantityDifferenceForEntitlements: number;
+	currentEpochMs: number;
+}) => {
+	const { org } = ctx;
+	const customerEntitlements = cusProductToCusEnts({ customerProduct });
+
+	const prepaidCustomerEntitlement = findPrepaidCustomerEntitlement({
+		customerEntitlements,
+		feature,
+	});
+
+	if (!prepaidCustomerEntitlement) {
+		throw new InternalError({
+			message: `[Quantity Update] Prepaid customer entitlement not found for feature: ${feature.internal_id}`,
+		});
+	}
+
+	const customerPrice = cusEntToCusPrice({
+		cusEnt: prepaidCustomerEntitlement,
+	});
+
+	if (!customerPrice) {
+		throw new InternalError({
+			message: `[Quantity Update] Prepaid customer price not found for feature: ${feature.internal_id}`,
+		});
+	}
+
+	// New customer entitlement
+	const newCustomerEntitlement = structuredClone(prepaidCustomerEntitlement);
+	newCustomerEntitlement.balance = new Decimal(
+		newCustomerEntitlement.balance ?? 0,
+	)
+		.add(quantityDifferenceForEntitlements) // does this include billing units?
+		.toNumber();
+
+	const lineItemContext: LineItemContext = {
+		price: customerPrice?.price,
+		product: customerProduct.product,
+		feature,
+		currency: orgToCurrency({ org }),
+		direction: "charge",
+		now: currentEpochMs,
+		billingTiming: "in_arrear",
+		billingPeriod,
+	};
+
+	const refundLineItem = usagePriceToLineItem({
+		cusEnt: newCustomerEntitlement,
+		context: {
+			...lineItemContext,
+			direction: "refund",
+		},
+	});
+
+	const chargeLineItem = usagePriceToLineItem({
+		cusEnt: prepaidCustomerEntitlement,
+		context: lineItemContext,
+	});
+
+	return [refundLineItem, chargeLineItem];
+};
diff --git a/server/src/internal/billing/v2/subscriptionUpdate/compute/computeQuantityUpdateDetails.ts b/server/src/internal/billing/v2/subscriptionUpdate/compute/computeQuantityUpdateDetails.ts
index f10fd141f..85099e421 100644
--- a/server/src/internal/billing/v2/subscriptionUpdate/compute/computeQuantityUpdateDetails.ts
+++ b/server/src/internal/billing/v2/subscriptionUpdate/compute/computeQuantityUpdateDetails.ts
@@ -1,9 +1,9 @@
 import {
 	cusProductToProduct,
 	extractBillingPeriod,
-	type Feature,
 	type FeatureOptions,
 	type FullCusProduct,
+	findFeatureByInternalId,
 	InternalError,
 } from "@autumn/shared";
 import { usagePriceToLineDescription } from "@autumn/shared/utils/billingUtils/invoicingUtils/descriptionUtils/usagePriceToLineDescription";
@@ -46,7 +46,7 @@ export const computeQuantityUpdateDetails = ({
 	stripeSubscription: Stripe.Subscription;
 	currentEpochMs: number;
 }): QuantityUpdateDetails => {
-	const { features } = ctx;
+	const { features, org } = ctx;
 
 	const internalFeatureId = updatedOptions.internal_feature_id;
 	const featureId = updatedOptions.feature_id;
@@ -57,6 +57,17 @@ export const computeQuantityUpdateDetails = ({
 		});
 	}
 
+	const feature = findFeatureByInternalId({
+		features,
+		internalId: internalFeatureId,
+	});
+
+	if (!feature) {
+		throw new InternalError({
+			message: `[Quantity Update] Feature not found for internal_id: ${internalFeatureId}`,
+		});
+	}
+
 	const quantityDifferences = calculateQuantityDifferences({
 		previousOptions,
 		updatedOptions,
@@ -85,16 +96,6 @@ export const computeQuantityUpdateDetails = ({
 		},
 	});
 
-	const feature = features.find(
-		(featureItem: Feature) => featureItem.internal_id === internalFeatureId,
-	);
-
-	if (!feature) {
-		throw new InternalError({
-			message: `[Quantity Update] Feature not found for internal_id: ${internalFeatureId}`,
-		});
-	}
-
 	const product = cusProductToProduct({ cusProduct: customerProduct });
 
 	const stripeInvoiceItemDescription = usagePriceToLineDescription({
diff --git a/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeInvoiceAction.ts b/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeInvoiceAction.ts
new file mode 100644
index 000000000..397a1e702
--- /dev/null
+++ b/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeInvoiceAction.ts
@@ -0,0 +1,74 @@
+import {
+	type FullCusProduct,
+	isCusProductTrialing,
+	isCustomerProductFree,
+	isCustomerProductOneOff,
+} from "@autumn/shared";
+import type { AutumnContext } from "@/honoUtils/HonoEnv";
+import type {
+	StripeInvoiceAction,
+	StripeSubscriptionAction,
+} from "@/internal/billing/v2/billingPlan";
+import { buildAutumnLineItems } from "@/internal/billing/v2/compute/computeAutumnUtils/buildAutumnLineItems";
+import type { UpdateSubscriptionContext } from "@/internal/billing/v2/subscriptionUpdate/fetch/updateSubscriptionContextSchema";
+import { lineItemsToStripeLines } from "@/internal/billing/v2/utils/stripeAdapter/invoiceLines/lineItemsToStripeLines";
+
+export const computeInvoiceAction = ({
+	ctx,
+	billingContext,
+	newCustomerProduct,
+	stripeSubscriptionAction,
+	billingCycleAnchor,
+}: {
+	ctx: AutumnContext;
+	billingContext: UpdateSubscriptionContext;
+	newCustomerProduct: FullCusProduct;
+	stripeSubscriptionAction?: StripeSubscriptionAction;
+	billingCycleAnchor?: number;
+}): StripeInvoiceAction | undefined => {
+	if (isCusProductTrialing({ cusProduct: newCustomerProduct })) {
+		return undefined;
+	}
+
+	/**
+	 * Cases:
+	 * One off -> Recurring (subscription created)
+	 * One off -> Free...? (no subscription action)
+	 * Free -> Recurring (subscription created)
+	 * Free -> One off (invoice needed...?)
+	 * Recurring -> Free (subscription canceled)
+	 * Recurring -> One off (subscription canceled... need... invoice?)
+	 */
+
+	const fromCustomerProduct = billingContext.customerProduct;
+	const toCustomerProduct = newCustomerProduct;
+
+	if (
+		isCustomerProductFree(fromCustomerProduct) &&
+		isCustomerProductOneOff(toCustomerProduct)
+	) {
+		return undefined;
+	}
+
+	// If subscription action is update, we need to create an invoice
+	const stripeSubscriptionActionType = stripeSubscriptionAction?.type;
+	if (stripeSubscriptionActionType === "update") {
+		const autumnLineItems = buildAutumnLineItems({
+			ctx,
+			newCusProducts: [toCustomerProduct],
+			ongoingCustomerProduct: fromCustomerProduct,
+			billingCycleAnchor,
+			testClockFrozenTime: billingContext.testClockFrozenTime,
+		});
+
+		const addLineParams = lineItemsToStripeLines({
+			lineItems: autumnLineItems,
+		});
+
+		return {
+			addLineParams: {
+				lines: addLineParams,
+			},
+		};
+	}
+};
diff --git a/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateCustomPlan.ts b/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateCustomPlan.ts
index 78702e74c..9d148a75d 100644
--- a/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateCustomPlan.ts
+++ b/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateCustomPlan.ts
@@ -2,18 +2,16 @@ import {
 	CusProductStatus,
 	cusProductToProduct,
 	type SubscriptionUpdateV0Params,
+	secondsToMs,
 } from "@autumn/shared";
 import type { AutumnContext } from "@server/honoUtils/HonoEnv";
 import type { UpdateSubscriptionContext } from "@server/internal/billing/v2/subscriptionUpdate/fetch/updateSubscriptionContextSchema";
 import type { BillingPlan } from "@/internal/billing/v2/billingPlan";
-import { addStripeSubscriptionIdToBillingPlan } from "@/internal/billing/v2/execute/addStripeSubscriptionIdToBillingPlan";
-import { executeAutumnBillingPlan } from "@/internal/billing/v2/execute/executeAutumnBillingPlan";
+import { computeInvoiceAction } from "@/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeInvoiceAction";
 import { computeSubscriptionUpdateFreeTrialPlan } from "@/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateFreeTrialPlan";
 import { computeSubscriptionUpdateNewCustomerProduct } from "@/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateNewCustomerProduct";
 import { computeSubscriptionUpdateStripeSubscriptionAction } from "@/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateStripeSubscriptionAction";
-import { logBillingPlan } from "@/internal/billing/v2/utils/logBillingPlan";
 import { createStripeResourcesForProducts } from "@/internal/billing/v2/utils/stripeAdapter/createStripeResourcesForProduct";
-import { executeStripeSubscriptionAction } from "@/internal/billing/v2/utils/stripeAdapter/subscriptions/executeStripeSubscriptionAction";
 import { computeCustomFullProduct } from "../../../compute/computeAutumnUtils/computeCustomFullProduct";
 
 export const computeSubscriptionUpdateCustomPlan = async ({
@@ -25,7 +23,7 @@ export const computeSubscriptionUpdateCustomPlan = async ({
 	updateSubscriptionContext: UpdateSubscriptionContext;
 	params: SubscriptionUpdateV0Params;
 }) => {
-	const { customerProduct } = updateSubscriptionContext;
+	const { customerProduct, stripeSubscription } = updateSubscriptionContext;
 
 	const currentFullProduct = cusProductToProduct({
 		cusProduct: customerProduct,
@@ -50,6 +48,10 @@ export const computeSubscriptionUpdateCustomPlan = async ({
 			fullProduct: customFullProduct,
 		});
 
+	const billingCycleAnchor =
+		freeTrialPlan.trialEndsAt ??
+		secondsToMs(stripeSubscription?.billing_cycle_anchor);
+
 	// 3. Compute the new customer product
 	const newFullCustomerProduct = computeSubscriptionUpdateNewCustomerProduct({
 		ctx,
@@ -57,6 +59,7 @@ export const computeSubscriptionUpdateCustomPlan = async ({
 		params,
 		fullProduct: customFullProduct,
 		freeTrialPlan,
+		billingCycleAnchor,
 	});
 
 	// 4. Create stripe prices
@@ -76,9 +79,18 @@ export const computeSubscriptionUpdateCustomPlan = async ({
 			freeTrialPlan,
 		});
 
+	const stripeInvoiceAction = computeInvoiceAction({
+		ctx,
+		billingContext: updateSubscriptionContext,
+		newCustomerProduct: newFullCustomerProduct,
+		stripeSubscriptionAction,
+		billingCycleAnchor,
+	});
+
 	const billingPlan: BillingPlan = {
 		stripe: {
-			subscription: stripeSubscriptionAction,
+			subscriptionAction: stripeSubscriptionAction,
+			invoiceAction: stripeInvoiceAction,
 		},
 		autumn: {
 			insertCustomerProducts: [newFullCustomerProduct],
@@ -96,26 +108,51 @@ export const computeSubscriptionUpdateCustomPlan = async ({
 		},
 	};
 
-	logBillingPlan({ ctx, billingPlan });
-
-	if (stripeSubscriptionAction) {
-		const updatedStripeSubscription = await executeStripeSubscriptionAction({
-			ctx,
-			subscriptionAction: stripeSubscriptionAction,
-		});
-
-		if (updatedStripeSubscription) {
-			addStripeSubscriptionIdToBillingPlan({
-				billingPlan,
-				stripeSubscriptionId: updatedStripeSubscription.id,
-			});
-		}
-	}
-
-	await executeAutumnBillingPlan({
-		ctx,
-		autumnBillingPlan: billingPlan.autumn,
-	});
-
 	return billingPlan;
+
+	// logBillingPlan({ ctx, billingPlan });
+
+	// if (stripeInvoiceAction) {
+	// 	const result = await executeStripeInvoiceAction({
+	// 		ctx,
+	// 		billingContext: updateSubscriptionContext,
+	// 		stripeInvoiceAction,
+	// 	});
+
+	// 	if (result.invoice) {
+	// 		await upsertInvoiceFromBilling({
+	// 			ctx,
+	// 			stripeInvoice: result.invoice,
+	// 			fullProducts: [customFullProduct],
+	// 			fullCustomer: fullCustomer,
+	// 		});
+	// 	}
+	// }
+
+	// if (stripeSubscriptionAction) {
+	// 	const stripeSubscription = await executeStripeSubscriptionAction({
+	// 		ctx,
+	// 		subscriptionAction: stripeSubscriptionAction,
+	// 	});
+
+	// 	if (stripeSubscription) {
+	// 		addStripeSubscriptionIdToBillingPlan({
+	// 			billingPlan,
+	// 			stripeSubscriptionId: stripeSubscription.id,
+	// 		});
+
+	// 		// Add subscription to DB
+	// 		await upsertSubscriptionFromBilling({
+	// 			ctx,
+	// 			stripeSubscription,
+	// 		});
+	// 	}
+	// }
+
+	// await executeAutumnBillingPlan({
+	// 	ctx,
+	// 	autumnBillingPlan: billingPlan.autumn,
+	// });
+
+	// return billingPlan;
 };
diff --git a/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateNewCustomerProduct.ts b/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateNewCustomerProduct.ts
index 2e02815be..bc2063029 100644
--- a/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateNewCustomerProduct.ts
+++ b/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateNewCustomerProduct.ts
@@ -1,8 +1,4 @@
-import {
-	type FullProduct,
-	type SubscriptionUpdateV0Params,
-	secondsToMs,
-} from "@autumn/shared";
+import type { FullProduct, SubscriptionUpdateV0Params } from "@autumn/shared";
 import type { AutumnContext } from "@/honoUtils/HonoEnv";
 import type { FreeTrialPlan } from "@/internal/billing/v2/billingPlan";
 import { computeSubscriptionUpdateFeatureQuantities } from "@/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateFeatureQuantities";
@@ -17,12 +13,14 @@ export const computeSubscriptionUpdateNewCustomerProduct = ({
 	updateSubscriptionContext,
 	fullProduct,
 	freeTrialPlan,
+	billingCycleAnchor,
 }: {
 	ctx: AutumnContext;
 	params: SubscriptionUpdateV0Params;
 	updateSubscriptionContext: UpdateSubscriptionContext;
 	fullProduct: FullProduct;
 	freeTrialPlan: FreeTrialPlan;
+	billingCycleAnchor?: number;
 }) => {
 	const {
 		customerProduct,
@@ -48,11 +46,6 @@ export const computeSubscriptionUpdateNewCustomerProduct = ({
 		params,
 	});
 
-	// TODO: Move this to a separate function
-	const billingCycleAnchor =
-		freeTrialPlan.trialEndsAt ??
-		secondsToMs(stripeSubscription?.billing_cycle_anchor);
-
 	const now = updateSubscriptionContext.testClockFrozenTime ?? Date.now();
 
 	// 1. Compute the new full customer product
diff --git a/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdatePlan.ts b/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdatePlan.ts
index f3b5f8ae7..86587c1ac 100644
--- a/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdatePlan.ts
+++ b/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdatePlan.ts
@@ -1,9 +1,10 @@
 import type { SubscriptionUpdateV0Params } from "@shared/index";
 import type { AutumnContext } from "@/honoUtils/HonoEnv";
-import type { SubscriptionUpdatePlan } from "../../typesOld";
+import { computeSubscriptionUpdateCustomPlan } from "@/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateCustomPlan/computeSubscriptionUpdateCustomPlan";
+import { computeSubscriptionUpdateQuantityPlan } from "@/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateQuantityPlan";
+import { SubscriptionUpdateIntentEnum } from "@/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateSchema";
 import type { UpdateSubscriptionContext } from "../fetch/updateSubscriptionContextSchema";
 import { computeSubscriptionUpdateIntent } from "./computeSubscriptionUpdateIntent";
-import { getComputeSubscriptionUpdatePlanFunction } from "./computeSubscriptionUpdatePlanIntentMap";
 
 /**
  * Compute the subscription update plan
@@ -11,7 +12,7 @@ import { getComputeSubscriptionUpdatePlanFunction } from "./computeSubscriptionU
  * @param params - The parameters for the subscription update
  * @returns The subscription update plan
  */
-export const computeSubscriptionUpdatePlan = ({
+export const computeSubscriptionUpdatePlan = async ({
 	ctx,
 	updateSubscriptionContext,
 	params,
@@ -19,9 +20,21 @@ export const computeSubscriptionUpdatePlan = ({
 	ctx: AutumnContext;
 	updateSubscriptionContext: UpdateSubscriptionContext;
 	params: SubscriptionUpdateV0Params;
-}): SubscriptionUpdatePlan => {
+}) => {
 	const intent = computeSubscriptionUpdateIntent(params);
-	const computePlan = getComputeSubscriptionUpdatePlanFunction(intent);
 
-	return computePlan({ ctx, updateSubscriptionContext, params });
+	switch (intent) {
+		case SubscriptionUpdateIntentEnum.UpdateQuantity:
+			return computeSubscriptionUpdateQuantityPlan({
+				ctx,
+				updateSubscriptionContext,
+				params,
+			});
+		case SubscriptionUpdateIntentEnum.UpdatePlan:
+			return await computeSubscriptionUpdateCustomPlan({
+				ctx,
+				updateSubscriptionContext,
+				params,
+			});
+	}
 };
diff --git a/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateQuantityPlan.ts b/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateQuantityPlan.ts
index 1ac84a04f..bcaf71e49 100644
--- a/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateQuantityPlan.ts
+++ b/server/src/internal/billing/v2/subscriptionUpdate/compute/computeSubscriptionUpdateQuantityPlan.ts
@@ -1,8 +1,9 @@
 import {
+	InternalError,
 	OngoingCusProductActionEnum,
 	type SubscriptionUpdateV0Params,
 	secondsToMs,
-} from "@shared/index";
+} from "@autumn/shared";
 import type { AutumnContext } from "@/honoUtils/HonoEnv";
 import { buildAutumnLineItems } from "../../compute/computeAutumnUtils/buildAutumnLineItems";
 import type { SubscriptionUpdateQuantityPlan } from "../../typesOld";
@@ -28,6 +29,12 @@ export const computeSubscriptionUpdateQuantityPlan = ({
 		paymentMethod,
 	} = updateSubscriptionContext;
 
+	if (!stripeSubscription) {
+		throw new InternalError({
+			message: `[Subscription Update] Stripe subscription not found`,
+		});
+	}
+
 	const featureQuantities = {
 		old: customerProduct.options,
 		new: params.options || [],
diff --git a/server/src/internal/billing/v2/subscriptionUpdate/handleSubscriptionUpdatePreview.ts b/server/src/internal/billing/v2/subscriptionUpdate/handleSubscriptionUpdatePreview.ts
new file mode 100644
index 000000000..0e626fea3
--- /dev/null
+++ b/server/src/internal/billing/v2/subscriptionUpdate/handleSubscriptionUpdatePreview.ts
@@ -0,0 +1,25 @@
+import { SubscriptionUpdateV0ParamsSchema } from "@autumn/shared";
+import { createRoute } from "../../../../honoMiddlewares/routeHandler";
+import { computeSubscriptionUpdatePlan } from "../subscriptionUpdate/compute/computeSubscriptionUpdatePlan";
+import { fetchApiSubscriptionUpdateContext } from "../subscriptionUpdate/fetch/fetchApiSubscriptionUpdateContext";
+
+export const handleSubscriptionUpdatePreview = createRoute({
+	body: SubscriptionUpdateV0ParamsSchema,
+	handler: async (c) => {
+		const ctx = c.get("ctx");
+		const body = c.req.valid("json");
+
+		const updateSubscriptionContext = await fetchApiSubscriptionUpdateContext({
+			ctx,
+			params: body,
+		});
+
+		const subscriptionUpdatePlan = await computeSubscriptionUpdatePlan({
+			ctx,
+			updateSubscriptionContext,
+			params: body,
+		});
+
+		return c.json(subscriptionUpdatePlan, 200);
+	},
+});
diff --git a/server/src/internal/billing/v2/typesOld.ts b/server/src/internal/billing/v2/typesOld.ts
index f125bde2c..7e43b91ce 100644
--- a/server/src/internal/billing/v2/typesOld.ts
+++ b/server/src/internal/billing/v2/typesOld.ts
@@ -40,11 +40,6 @@ export type StripeSubAction = {
 	items?: Stripe.SubscriptionUpdateParams.Item[];
 };
 
-export type StripeInvoiceAction = {
-	items: Stripe.InvoiceAddLinesParams.Line[];
-	onPaymentFailure: "return_url" | "checkout_session";
-};
-
 export type StripeCheckoutAction = {
 	shouldCreate: boolean;
 	reason?: string;
diff --git a/server/src/internal/billing/v2/utils/logBillingPlan.ts b/server/src/internal/billing/v2/utils/logBillingPlan.ts
index 99d252b7b..99dff2034 100644
--- a/server/src/internal/billing/v2/utils/logBillingPlan.ts
+++ b/server/src/internal/billing/v2/utils/logBillingPlan.ts
@@ -34,20 +34,6 @@ export const logBillingPlan = ({
 					}
 				: undefined,
 		},
-		stripe: {
-			subscription: billingPlan.stripe.subscription
-				? {
-						type: billingPlan.stripe.subscription.type,
-						stripeSubscriptionId:
-							billingPlan.stripe.subscription.type !== "create"
-								? billingPlan.stripe.subscription.stripeSubscriptionId
-								: undefined,
-						params:
-							billingPlan.stripe.subscription.type !== "cancel"
-								? billingPlan.stripe.subscription.params
-								: undefined,
-					}
-				: undefined,
-		},
+		stripe: billingPlan.stripe,
 	});
 };
diff --git a/server/src/internal/billing/v2/utils/stripeAdapter/applyStripeDiscounts/applyAmountOffDiscountToLineItems.ts b/server/src/internal/billing/v2/utils/stripeAdapter/discounts/applyAmountOffDiscountToLineItems.ts
similarity index 100%
rename from server/src/internal/billing/v2/utils/stripeAdapter/applyStripeDiscounts/applyAmountOffDiscountToLineItems.ts
rename to server/src/internal/billing/v2/utils/stripeAdapter/discounts/applyAmountOffDiscountToLineItems.ts
diff --git a/server/src/internal/billing/v2/utils/stripeAdapter/applyStripeDiscounts/applyPercentOffDiscountToLineItems.ts b/server/src/internal/billing/v2/utils/stripeAdapter/discounts/applyPercentOffDiscountToLineItems.ts
similarity index 100%
rename from server/src/internal/billing/v2/utils/stripeAdapter/applyStripeDiscounts/applyPercentOffDiscountToLineItems.ts
rename to server/src/internal/billing/v2/utils/stripeAdapter/discounts/applyPercentOffDiscountToLineItems.ts
diff --git a/server/src/internal/billing/v2/utils/stripeAdapter/applyStripeDiscounts/applyStripeDiscountsToLineItems.ts b/server/src/internal/billing/v2/utils/stripeAdapter/discounts/applyStripeDiscountsToLineItems.ts
similarity index 100%
rename from server/src/internal/billing/v2/utils/stripeAdapter/applyStripeDiscounts/applyStripeDiscountsToLineItems.ts
rename to server/src/internal/billing/v2/utils/stripeAdapter/discounts/applyStripeDiscountsToLineItems.ts
diff --git a/server/src/internal/billing/v2/utils/stripeAdapter/applyStripeDiscounts/discountAppliesToLineItem.ts b/server/src/internal/billing/v2/utils/stripeAdapter/discounts/discountAppliesToLineItem.ts
similarity index 100%
rename from server/src/internal/billing/v2/utils/stripeAdapter/applyStripeDiscounts/discountAppliesToLineItem.ts
rename to server/src/internal/billing/v2/utils/stripeAdapter/discounts/discountAppliesToLineItem.ts
diff --git a/server/src/internal/billing/v2/utils/stripeAdapter/applyStripeDiscounts/subToDiscounts.ts b/server/src/internal/billing/v2/utils/stripeAdapter/discounts/subToDiscounts.ts
similarity index 100%
rename from server/src/internal/billing/v2/utils/stripeAdapter/applyStripeDiscounts/subToDiscounts.ts
rename to server/src/internal/billing/v2/utils/stripeAdapter/discounts/subToDiscounts.ts
diff --git a/server/src/internal/billing/v2/utils/stripeAdapter/stripeInvoiceOps/lineItemsToStripeLines.ts b/server/src/internal/billing/v2/utils/stripeAdapter/invoiceLines/lineItemsToStripeLines.ts
similarity index 100%
rename from server/src/internal/billing/v2/utils/stripeAdapter/stripeInvoiceOps/lineItemsToStripeLines.ts
rename to server/src/internal/billing/v2/utils/stripeAdapter/invoiceLines/lineItemsToStripeLines.ts
diff --git a/server/src/internal/billing/v2/utils/stripeAdapter/subscriptions/buildStripeSubscriptionUpdateAction.ts b/server/src/internal/billing/v2/utils/stripeAdapter/subscriptions/buildStripeSubscriptionUpdateAction.ts
index 60343ca3b..0d918ce0c 100644
--- a/server/src/internal/billing/v2/utils/stripeAdapter/subscriptions/buildStripeSubscriptionUpdateAction.ts
+++ b/server/src/internal/billing/v2/utils/stripeAdapter/subscriptions/buildStripeSubscriptionUpdateAction.ts
@@ -1,6 +1,6 @@
 import { msToSeconds } from "@shared/utils/common/unixUtils";
 import type Stripe from "stripe";
-import { isStripeSubscriptionCancelling } from "@/external/stripe/subscriptions/utils/classifyStripeSubscriptionUtils";
+import { isStripeSubscriptionCanceling } from "@/external/stripe/subscriptions/utils/classifyStripeSubscriptionUtils";
 import type { AutumnContext } from "@/honoUtils/HonoEnv";
 import type { BillingContext } from "@/internal/billing/v2/billingContext";
 import type { FreeTrialPlan } from "@/internal/billing/v2/billingPlan";
@@ -25,7 +25,7 @@ export const buildStripeSubscriptionUpdateAction = ({
 	}
 
 	const trialEndsAt = freeTrialPlan?.trialEndsAt;
-	const cancelAtPeriodEnd = isStripeSubscriptionCancelling(stripeSubscription)
+	const cancelAtPeriodEnd = isStripeSubscriptionCanceling(stripeSubscription)
 		? false
 		: undefined;
 
diff --git a/server/src/internal/billing/v2/utils/upsertInvoiceFromBilling.ts b/server/src/internal/billing/v2/utils/upsertInvoiceFromBilling.ts
new file mode 100644
index 000000000..5b8cd4ff1
--- /dev/null
+++ b/server/src/internal/billing/v2/utils/upsertInvoiceFromBilling.ts
@@ -0,0 +1,55 @@
+import type { FullCustomer, FullProduct } from "@autumn/shared";
+import type Stripe from "stripe";
+import type { AutumnContext } from "@/honoUtils/HonoEnv";
+import { InvoiceService } from "@/internal/invoices/InvoiceService";
+import { getInvoiceItems } from "@/internal/invoices/invoiceUtils";
+
+export const upsertInvoiceFromBilling = async ({
+	ctx,
+	stripeInvoice,
+	fullProducts,
+	fullCustomer,
+}: {
+	ctx: AutumnContext;
+	stripeInvoice: Stripe.Invoice;
+	fullProducts: FullProduct[];
+	fullCustomer: FullCustomer;
+}) => {
+	const productIds = fullProducts.map((p) => p.id);
+	const internalProductIds = fullProducts.map((p) => p.internal_id);
+
+	const internalCustomerId = fullCustomer.internal_id;
+	const internalEntityId = fullCustomer.entity?.internal_id;
+
+	const autumnInvoiceItems = await getInvoiceItems({
+		stripeInvoice,
+		prices: fullProducts.flatMap((p) => p.prices),
+		logger: ctx.logger,
+	});
+
+	// 1. Check if invoice exists in Autumn
+	const updatedInvoice = await InvoiceService.updateByStripeId({
+		db: ctx.db,
+		stripeId: stripeInvoice.id,
+		updates: {
+			product_ids: productIds,
+			internal_product_ids: internalProductIds,
+		},
+	});
+
+	if (updatedInvoice) return;
+
+	// 2. Create invoice
+	const newInvoice = await InvoiceService.createInvoiceFromStripe({
+		db: ctx.db,
+		stripeInvoice,
+		internalCustomerId,
+		internalEntityId,
+		org: ctx.org,
+		productIds,
+		internalProductIds,
+		items: autumnInvoiceItems,
+	});
+
+	return newInvoice;
+};
diff --git a/server/src/internal/billing/v2/utils/upsertSubscriptionFromBilling.ts b/server/src/internal/billing/v2/utils/upsertSubscriptionFromBilling.ts
new file mode 100644
index 000000000..3d74775a1
--- /dev/null
+++ b/server/src/internal/billing/v2/utils/upsertSubscriptionFromBilling.ts
@@ -0,0 +1,42 @@
+import type Stripe from "stripe";
+import {
+	getEarliestPeriodEnd,
+	getLatestPeriodStart,
+} from "@/external/stripe/stripeSubUtils/convertSubUtils";
+import type { AutumnContext } from "@/honoUtils/HonoEnv";
+import { SubService } from "@/internal/subscriptions/SubService";
+import { generateId } from "@/utils/genUtils";
+
+export const upsertSubscriptionFromBilling = async ({
+	ctx,
+	stripeSubscription,
+}: {
+	ctx: AutumnContext;
+	stripeSubscription: Stripe.Subscription;
+}) => {
+	// Store
+	const earliestPeriodEnd = getEarliestPeriodEnd({ sub: stripeSubscription });
+	const currentPeriodStart = getLatestPeriodStart({ sub: stripeSubscription });
+
+	const updatedSubscription = await SubService.updateFromStripe({
+		db: ctx.db,
+		stripeSub: stripeSubscription,
+	});
+
+	if (updatedSubscription) return;
+
+	await SubService.createSub({
+		db: ctx.db,
+		sub: {
+			id: generateId("sub"),
+			stripe_id: stripeSubscription.id,
+			stripe_schedule_id: stripeSubscription.schedule as string,
+			created_at: stripeSubscription.created * 1000,
+			usage_features: [],
+			org_id: ctx.org.id,
+			env: ctx.env,
+			current_period_start: currentPeriodStart,
+			current_period_end: earliestPeriodEnd,
+		},
+	});
+};
diff --git a/server/src/internal/invoices/InvoiceService.ts b/server/src/internal/invoices/InvoiceService.ts
index 2246c9631..f87cd2e32 100644
--- a/server/src/internal/invoices/InvoiceService.ts
+++ b/server/src/internal/invoices/InvoiceService.ts
@@ -2,6 +2,7 @@ import {
 	type ApiInvoiceV1,
 	type Customer,
 	type Feature,
+	type InsertInvoice,
 	type Invoice,
 	type InvoiceItem,
 	type InvoiceStatus,
@@ -210,11 +211,11 @@ export class InvoiceService {
 	}: {
 		db: DrizzleCli;
 		stripeId: string;
-		updates: Partial<Invoice>;
+		updates: Partial<InsertInvoice>;
 	}) {
 		const results = await db
 			.update(invoices)
-			.set(updates as any)
+			.set(updates)
 			.where(eq(invoices.stripe_id, stripeId))
 			.returning();
 
diff --git a/server/src/internal/products/productUtils/productResponseUtils/getAttachScenario.ts b/server/src/internal/products/productUtils/productResponseUtils/getAttachScenario.ts
index 6e7ef5f24..223a60c04 100644
--- a/server/src/internal/products/productUtils/productResponseUtils/getAttachScenario.ts
+++ b/server/src/internal/products/productUtils/productResponseUtils/getAttachScenario.ts
@@ -3,7 +3,7 @@ import {
 	cusProductToProduct,
 	type FullCustomer,
 	type FullProduct,
-	isCusProductCanceled,
+	isCustomerProductCanceled,
 } from "@autumn/shared";
 
 import { getExistingCusProducts } from "@/internal/customers/cusProducts/cusProductUtils/getExistingCusProducts.js";
@@ -43,7 +43,7 @@ export const getAttachScenario = ({
 			curSameProduct &&
 			curSameProduct.product.id !== curScheduledProduct?.product.id
 		) {
-			if (isCusProductCanceled({ cusProduct: curSameProduct })) {
+			if (isCustomerProductCanceled(curSameProduct)) {
 				return AttachScenario.Renew;
 			} else {
 				return AttachScenario.Active;
@@ -59,7 +59,7 @@ export const getAttachScenario = ({
 
 	// 1. If current product is the same as the product, return active
 	if (curMainProduct?.product.id === fullProduct.id) {
-		if (isCusProductCanceled({ cusProduct: curMainProduct })) {
+		if (isCustomerProductCanceled(curMainProduct)) {
 			return AttachScenario.Renew;
 		} else return AttachScenario.Active;
 	}
diff --git a/shared/index.ts b/shared/index.ts
index 97feece8c..fab3ed602 100644
--- a/shared/index.ts
+++ b/shared/index.ts
@@ -100,7 +100,7 @@ export * from "./models/attachModels/attachFunctionResponse.js";
 export * from "./models/billingModels/cusProductActions.js";
 export * from "./models/billingModels/existingRollovers.js";
 export * from "./models/billingModels/existingUsages.js";
-
+export * from "./models/billingModels/index.js";
 export * from "./models/billingModels/initFullCustomerProductContext.js";
 export * from "./models/billingModels/invoicingModels/lineItem.js";
 // Billing Models
diff --git a/shared/models/billingModels/index.ts b/shared/models/billingModels/index.ts
index e69de29bb..16696ba2b 100644
--- a/shared/models/billingModels/index.ts
+++ b/shared/models/billingModels/index.ts
@@ -0,0 +1 @@
+export * from "./invoicingModels/lineItemContext";
diff --git a/shared/models/cusModels/invoiceModels/invoiceTable.ts b/shared/models/cusModels/invoiceModels/invoiceTable.ts
index 5b2eea154..963ea9628 100644
--- a/shared/models/cusModels/invoiceModels/invoiceTable.ts
+++ b/shared/models/cusModels/invoiceModels/invoiceTable.ts
@@ -1,9 +1,9 @@
+import type { InferInsertModel, InferSelectModel } from "drizzle-orm";
 import { foreignKey, jsonb, numeric, pgTable, text } from "drizzle-orm/pg-core";
 import { collatePgColumn, sqlNow } from "../../../db/utils.js";
-import { InvoiceDiscount, InvoiceItem } from "./invoiceModels.js";
 import { customers } from "../cusTable.js";
 import { entities } from "../entityModels/entityTable.js";
-import { InferSelectModel, InferInsertModel } from "drizzle-orm";
+import type { InvoiceDiscount, InvoiceItem } from "./invoiceModels.js";
 
 export const invoices = pgTable(
 	"invoices",
@@ -41,4 +41,4 @@ export const invoices = pgTable(
 collatePgColumn(invoices.id, "C");
 
 export type InvoiceRow = InferSelectModel<typeof invoices>;
-export type InsertInvoiceRow = InferInsertModel<typeof invoices>;
+export type InsertInvoice = InferInsertModel<typeof invoices>;
diff --git a/shared/utils/cusEntUtils/findCustomerEntitlement/findPrepaidCustomerEntitlement.ts b/shared/utils/cusEntUtils/findCustomerEntitlement/findPrepaidCustomerEntitlement.ts
new file mode 100644
index 000000000..1c030490d
--- /dev/null
+++ b/shared/utils/cusEntUtils/findCustomerEntitlement/findPrepaidCustomerEntitlement.ts
@@ -0,0 +1,19 @@
+import type { FullCusEntWithFullCusProduct } from "@models/cusProductModels/cusEntModels/cusEntWithProduct";
+import type { Feature } from "@models/featureModels/featureModels";
+import { isPrepaidCusEnt } from "@utils/cusEntUtils/cusEntUtils";
+import { cusEntMatchesFeature } from "@utils/cusEntUtils/filterCusEntUtils";
+
+export const findPrepaidCustomerEntitlement = ({
+	customerEntitlements,
+	feature,
+}: {
+	customerEntitlements: FullCusEntWithFullCusProduct[];
+	feature: Feature;
+}) => {
+	// 1. Get prepaid customer entitlement
+	return customerEntitlements.find(
+		(entitlement) =>
+			isPrepaidCusEnt({ cusEnt: entitlement }) &&
+			cusEntMatchesFeature({ cusEnt: entitlement, feature }),
+	);
+};
diff --git a/shared/utils/cusProductUtils/classifyCusProduct.ts b/shared/utils/cusProductUtils/classifyCusProduct.ts
index 5dbfaa46d..e8c446bcd 100644
--- a/shared/utils/cusProductUtils/classifyCusProduct.ts
+++ b/shared/utils/cusProductUtils/classifyCusProduct.ts
@@ -7,11 +7,7 @@ import { notNullish, nullish } from "../utils";
 import { cusProductToPrices } from "./convertCusProduct";
 import { ACTIVE_STATUSES } from "./cusProductConstants";
 
-export const isCusProductOneOff = ({
-	cusProduct,
-}: {
-	cusProduct?: FullCusProduct;
-}) => {
+export const isCustomerProductOneOff = (cusProduct?: FullCusProduct) => {
 	if (!cusProduct) return false;
 
 	const prices = cusProductToPrices({ cusProduct });
@@ -19,14 +15,18 @@ export const isCusProductOneOff = ({
 	return isOneOffProduct({ prices });
 };
 
-export const isCusProductCanceled = ({
-	cusProduct,
-}: {
-	cusProduct?: FullCusProduct;
-}) => {
+export const isCustomerProductCanceled = (cusProduct?: FullCusProduct) => {
 	if (!cusProduct) return false;
 
-	return cusProduct.canceled;
+	return notNullish(cusProduct.canceled_at);
+};
+
+export const isCustomerProductFree = (cusProduct?: FullCusProduct) => {
+	if (!cusProduct) return false;
+
+	const prices = cusProductToPrices({ cusProduct });
+
+	return isFreeProduct({ prices });
 };
 
 export const isCusProductTrialing = ({
diff --git a/shared/utils/cusProductUtils/convertCusProduct.ts b/shared/utils/cusProductUtils/convertCusProduct.ts
index bf19ddc44..39d837b20 100644
--- a/shared/utils/cusProductUtils/convertCusProduct.ts
+++ b/shared/utils/cusProductUtils/convertCusProduct.ts
@@ -163,3 +163,14 @@ export const cusProductToProduct = ({
 		free_trial: cusProduct.free_trial,
 	} as FullProduct;
 };
+
+export const cusProductToCusEnts = ({
+	customerProduct,
+}: {
+	customerProduct: FullCusProduct;
+}): FullCusEntWithFullCusProduct[] => {
+	return customerProduct.customer_entitlements.map((cusEnt) => ({
+		...cusEnt,
+		customer_product: customerProduct,
+	}));
+};
diff --git a/shared/utils/featureUtils/findFeatureUtils.ts b/shared/utils/featureUtils/findFeatureUtils.ts
new file mode 100644
index 000000000..55a8c5105
--- /dev/null
+++ b/shared/utils/featureUtils/findFeatureUtils.ts
@@ -0,0 +1,11 @@
+import type { Feature } from "@models/featureModels/featureModels";
+
+export const findFeatureByInternalId = ({
+	features,
+	internalId,
+}: {
+	features: Feature[];
+	internalId: string;
+}): Feature | undefined => {
+	return features.find((feature) => feature.internal_id === internalId);
+};
diff --git a/shared/utils/index.ts b/shared/utils/index.ts
index 3fcfcd0a8..e1d993998 100644
--- a/shared/utils/index.ts
+++ b/shared/utils/index.ts
@@ -24,6 +24,7 @@ export * from "./cusEntUtils/convertCusEntUtils/cusEntToCusPrice.js";
 export * from "./cusEntUtils/convertCusEntUtils.js";
 export * from "./cusEntUtils/cusEntUtils.js";
 export * from "./cusEntUtils/filterCusEntUtils.js";
+export * from "./cusEntUtils/findCustomerEntitlement/findPrepaidCustomerEntitlement.js";
 // Cus ent utils
 export * from "./cusEntUtils/getRolloverFields.js";
 export * from "./cusEntUtils/getStartingBalance.js";
@@ -47,6 +48,7 @@ export * from "./cusUtils/fullCusUtils/getCusStripeSubCount.js";
 export * from "./expandUtils.js";
 export * from "./featureUtils/apiFeatureToDbFeature.js";
 export * from "./featureUtils/convertFeatureUtils.js";
+export * from "./featureUtils/findFeatureUtils.js";
 // Feature utils
 export * from "./featureUtils.js";
 // INTERVAL UTILS
diff --git a/vite/src/hooks/stores/useSheetStore.ts b/vite/src/hooks/stores/useSheetStore.ts
index 3f8c0feda..84d97ec97 100644
--- a/vite/src/hooks/stores/useSheetStore.ts
+++ b/vite/src/hooks/stores/useSheetStore.ts
@@ -11,6 +11,7 @@ export type SheetType =
 	| "attach-product"
 	| "subscription-detail"
 	| "subscription-update"
+	| "subscription-update-test" // TEST: Remove this line to revert
 	| "balance-selection"
 	| "balance-edit"
 	| null;
diff --git a/vite/src/views/customers2/components/sheets/SubscriptionUpdateTestSheet.tsx b/vite/src/views/customers2/components/sheets/SubscriptionUpdateTestSheet.tsx
new file mode 100644
index 000000000..a7ddf5b35
--- /dev/null
+++ b/vite/src/views/customers2/components/sheets/SubscriptionUpdateTestSheet.tsx
@@ -0,0 +1,831 @@
+import {
+	type Entity,
+	type Feature,
+	type FrontendProduct,
+	type FullCusProduct,
+	type FullCustomer,
+	getProductItemDisplay,
+	type ProductItem,
+	type ProductV2,
+	type SubscriptionUpdateV0Params,
+	stripeToAtmnAmount,
+} from "@autumn/shared";
+import { PencilSimple } from "@phosphor-icons/react";
+import { useMutation, useQuery } from "@tanstack/react-query";
+import { useEffect, useMemo, useState } from "react";
+import { useNavigate } from "react-router";
+import { Button } from "@/components/v2/buttons/Button";
+import { IconButton } from "@/components/v2/buttons/IconButton";
+import { SheetHeader } from "@/components/v2/sheets/InlineSheet";
+import { usePrepaidItems } from "@/hooks/stores/useProductStore";
+import { useSheetStore } from "@/hooks/stores/useSheetStore";
+import { useSubscriptionById } from "@/hooks/stores/useSubscriptionStore";
+import { useAxiosInstance } from "@/services/useAxiosInstance";
+import { pushPage } from "@/utils/genUtils";
+import { useCusQuery } from "@/views/customers/customer/hooks/useCusQuery";
+
+/**
+ * TEST SHEET: SubscriptionUpdateTestSheet
+ *
+ * This is an isolated test sheet for testing the subscription update flow.
+ * It calls:
+ * - POST /v1/subscriptions/preview/update - to get a billing plan preview
+ * - POST /v1/subscriptions/update - to execute the update
+ *
+ * Usage: Open this sheet with an itemId (cusProduct id) and optional customizedProduct in data
+ */
+
+interface PrepaidEditorProps {
+	prepaidItems: Array<{
+		feature_id?: string | null;
+		feature?: { internal_id: string } | undefined;
+	}>;
+	prepaidOptions: Record<string, number>;
+	onPrepaidChange: (featureId: string, quantity: number) => void;
+}
+
+function PrepaidEditor({
+	prepaidItems,
+	prepaidOptions,
+	onPrepaidChange,
+}: PrepaidEditorProps) {
+	if (prepaidItems.length === 0) return null;
+
+	return (
+		<div className="border-b border-border">
+			<div className="px-4 py-2 border-b border-border">
+				<h3 className="text-sm font-medium">Prepaid Quantities</h3>
+			</div>
+			<div className="px-4 py-3 space-y-2">
+				{prepaidItems.map((item) => {
+					const featureId = item.feature_id ?? item.feature?.internal_id ?? "";
+					const inputId = `prepaid-${featureId}`;
+					return (
+						<div key={featureId} className="flex items-center gap-3">
+							<label
+								htmlFor={inputId}
+								className="text-sm text-t-secondary flex-1"
+							>
+								{featureId}
+							</label>
+							<input
+								id={inputId}
+								type="number"
+								min={0}
+								value={prepaidOptions[featureId] ?? 0}
+								onChange={(e) =>
+									onPrepaidChange(featureId, parseInt(e.target.value, 10) || 0)
+								}
+								className="w-20 px-2 py-1 border border-border rounded text-sm bg-transparent"
+							/>
+						</div>
+					);
+				})}
+			</div>
+		</div>
+	);
+}
+
+interface BillingPlanData {
+	autumn?: {
+		insertCustomerProducts?: Array<{
+			product?: { name?: string };
+			customer_entitlements?: Array<{
+				feature_id?: string;
+				balance?: number;
+				entitlement?: { feature?: { name?: string } };
+			}>;
+		}>;
+		updateCustomerProduct?: {
+			customerProduct?: { product?: { name?: string } };
+			updates?: Record<string, unknown>;
+		};
+		customPrices?: unknown[];
+		customEntitlements?: unknown[];
+	};
+	stripe?: {
+		subscriptionAction?: {
+			type?: string;
+			stripeSubscriptionId?: string;
+			params?: {
+				items?: Array<{
+					id?: string;
+					price?: string;
+					quantity?: number;
+					deleted?: boolean;
+				}>;
+				trial_end?: number;
+				proration_behavior?: string;
+				cancel_at_period_end?: boolean;
+			};
+		};
+		invoiceAction?: {
+			addLineParams?: {
+				lines?: Array<{
+					description?: string;
+					amount?: number;
+				}>;
+			};
+		};
+	};
+}
+
+interface PreviewResultProps {
+	data: unknown;
+	isLoading: boolean;
+	error: Error | null;
+}
+
+function PreviewResult({ data, isLoading, error }: PreviewResultProps) {
+	const billingPlan = data as BillingPlanData | null;
+
+	return (
+		<div className="border-b border-border">
+			<div className="px-4 py-2 border-b border-border">
+				<h3 className="text-sm font-medium">Billing Plan Preview</h3>
+			</div>
+
+			{isLoading ? (
+				<div className="px-4 py-3 text-sm text-t-secondary">
+					Loading preview...
+				</div>
+			) : null}
+
+			{error ? (
+				<div className="px-4 py-3 text-sm text-red-400">
+					Error: {error.message}
+				</div>
+			) : null}
+
+			{!data && !isLoading && !error ? (
+				<div className="px-4 py-3 text-sm text-t-secondary">
+					No preview data yet
+				</div>
+			) : null}
+
+			{billingPlan && !isLoading ? (
+				<div className="divide-y divide-border">
+					{/* Insert Customer Products */}
+					{billingPlan.autumn?.insertCustomerProducts &&
+					billingPlan.autumn.insertCustomerProducts.length > 0 ? (
+						<div className="px-4 py-3 border-l-2 border-l-green-500">
+							<h4 className="text-xs font-semibold text-green-400 mb-1">
+								📥 Inserting Customer Product
+							</h4>
+							{billingPlan.autumn.insertCustomerProducts.map((cp, index) => (
+								<div key={index} className="text-sm">
+									<div className="font-medium">
+										{cp.product?.name || "Unknown Product"}
+									</div>
+									{cp.customer_entitlements &&
+									cp.customer_entitlements.length > 0 ? (
+										<div className="mt-1 text-xs text-t-secondary">
+											<span className="font-medium">Balances: </span>
+											{cp.customer_entitlements.map((ent, entIndex) => (
+												<span key={entIndex}>
+													{ent.entitlement?.feature?.name || ent.feature_id}:{" "}
+													{ent.balance}
+													{entIndex <
+													(cp.customer_entitlements?.length ?? 0) - 1
+														? ", "
+														: ""}
+												</span>
+											))}
+										</div>
+									) : null}
+								</div>
+							))}
+						</div>
+					) : null}
+
+					{/* Update Customer Product */}
+					{(() => {
+						const updateCusProduct = billingPlan.autumn?.updateCustomerProduct;
+						if (!updateCusProduct) return null;
+						return (
+							<div className="px-4 py-3 border-l-2 border-l-amber-500">
+								<h4 className="text-xs font-semibold text-amber-400 mb-1">
+									✏️ Updating Customer Product
+								</h4>
+								<div className="text-sm">
+									<div className="font-medium">
+										{updateCusProduct.customerProduct?.product?.name ||
+											"Unknown Product"}
+									</div>
+									{updateCusProduct.updates ? (
+										<div className="mt-1 text-xs text-t-secondary">
+											<span className="font-medium">Updates: </span>
+											<code className="text-amber-400">
+												{JSON.stringify(updateCusProduct.updates)}
+											</code>
+										</div>
+									) : null}
+								</div>
+							</div>
+						);
+					})()}
+
+					{/* Stripe Subscription Action */}
+					{billingPlan.stripe?.subscriptionAction ? (
+						<div className="px-4 py-3 border-l-2 border-l-blue-500">
+							<h4 className="text-xs font-semibold text-blue-400 mb-1">
+								💳 Stripe Subscription Action
+							</h4>
+							<div className="text-sm flex items-center gap-3">
+								<span>
+									<span className="text-t-secondary">Type: </span>
+									<span className="font-medium">
+										{billingPlan.stripe.subscriptionAction.type || "none"}
+									</span>
+								</span>
+								{billingPlan.stripe.subscriptionAction.stripeSubscriptionId ? (
+									<span>
+										<span className="text-t-secondary">Sub: </span>
+										<code className="text-xs text-blue-400">
+											{
+												billingPlan.stripe.subscriptionAction
+													.stripeSubscriptionId
+											}
+										</code>
+									</span>
+								) : null}
+							</div>
+							{/* Subscription Items */}
+							{billingPlan.stripe.subscriptionAction.params?.items &&
+							billingPlan.stripe.subscriptionAction.params.items.length > 0 ? (
+								<div className="mt-2 space-y-1">
+									<div className="text-xs text-t-secondary font-medium">
+										Items:
+									</div>
+									{billingPlan.stripe.subscriptionAction.params.items.map(
+										(item, index) => (
+											<div
+												key={index}
+												className={`flex justify-between text-xs pl-2 border-l ${
+													item.deleted
+														? "border-red-500/30"
+														: "border-blue-500/30"
+												}`}
+											>
+												{item.deleted ? (
+													<>
+														<span className="text-red-400 font-mono">
+															{item.id || "Unknown item"}
+														</span>
+														<span className="text-red-400">🗑️ delete</span>
+													</>
+												) : (
+													<>
+														<span className="text-t-primary font-mono">
+															{item.price || item.id || "Unknown"}
+														</span>
+														<span className="text-blue-400">
+															qty: {item.quantity ?? 1}
+														</span>
+													</>
+												)}
+											</div>
+										),
+									)}
+								</div>
+							) : null}
+							{/* Other params */}
+							{billingPlan.stripe.subscriptionAction.params?.trial_end ? (
+								<div className="mt-1 text-xs text-t-secondary">
+									<span>Trial ends: </span>
+									<span className="text-green-400">
+										{new Date(
+											billingPlan.stripe.subscriptionAction.params.trial_end *
+												1000,
+										).toLocaleDateString()}
+									</span>
+								</div>
+							) : null}
+							{billingPlan.stripe.subscriptionAction.params ? (
+								<details className="mt-1">
+									<summary className="text-xs cursor-pointer text-t-secondary hover:text-t-primary">
+										View raw params
+									</summary>
+									<pre className="text-xs bg-t-50 p-2 rounded mt-1 overflow-auto max-h-32">
+										{JSON.stringify(
+											billingPlan.stripe.subscriptionAction.params,
+											null,
+											2,
+										)}
+									</pre>
+								</details>
+							) : null}
+						</div>
+					) : null}
+
+					{/* Stripe Invoice Action */}
+					{billingPlan.stripe?.invoiceAction ? (
+						<div className="px-4 py-3 border-l-2 border-l-purple-500">
+							<h4 className="text-xs font-semibold text-purple-400 mb-1">
+								🧾 Stripe Invoice Action
+							</h4>
+							{billingPlan.stripe.invoiceAction.addLineParams?.lines &&
+							billingPlan.stripe.invoiceAction.addLineParams.lines.length >
+								0 ? (
+								<div className="space-y-1">
+									{billingPlan.stripe.invoiceAction.addLineParams.lines.map(
+										(
+											line: {
+												description?: string;
+												amount?: number;
+											},
+											index: number,
+										) => {
+											const amount = line.amount
+												? stripeToAtmnAmount({
+														amount: line.amount,
+														currency: "usd",
+													})
+												: 0;
+											return (
+												<div
+													key={index}
+													className="flex justify-between text-xs"
+												>
+													<span className="text-t-primary">
+														{line.description || "Line item"}
+													</span>
+													<span
+														className={
+															amount >= 0 ? "text-green-400" : "text-red-400"
+														}
+													>
+														${amount.toFixed(2)}
+													</span>
+												</div>
+											);
+										},
+									)}
+								</div>
+							) : (
+								<div className="text-xs text-t-secondary">No line items</div>
+							)}
+							<details className="mt-1">
+								<summary className="text-xs cursor-pointer text-t-secondary hover:text-t-primary">
+									View raw params
+								</summary>
+								<pre className="text-xs bg-t-50 p-2 rounded mt-1 overflow-auto max-h-32">
+									{JSON.stringify(billingPlan.stripe.invoiceAction, null, 2)}
+								</pre>
+							</details>
+						</div>
+					) : null}
+
+					{/* Empty Stripe section indicator */}
+					{billingPlan.stripe &&
+					!billingPlan.stripe.subscriptionAction &&
+					!billingPlan.stripe.invoiceAction ? (
+						<div className="px-4 py-2 text-xs text-t-secondary">
+							No Stripe actions required
+						</div>
+					) : null}
+
+					{/* Raw JSON toggle */}
+					<details className="px-4 py-2 text-xs">
+						<summary className="cursor-pointer text-t-secondary hover:text-t-primary">
+							View raw JSON
+						</summary>
+						<pre className="bg-t-50 p-2 rounded mt-1 overflow-auto max-h-40">
+							{JSON.stringify(data, null, 2)}
+						</pre>
+					</details>
+				</div>
+			) : null}
+		</div>
+	);
+}
+
+interface UpdateResultProps {
+	data: unknown;
+	isLoading: boolean;
+	error: Error | null;
+}
+
+function UpdateResult({ data, isLoading, error }: UpdateResultProps) {
+	if (!data && !isLoading && !error) return null;
+
+	return (
+		<div className="border-b border-border">
+			<div className="px-4 py-2 border-b border-border">
+				<h3 className="text-sm font-medium">Update Response</h3>
+			</div>
+			{isLoading ? (
+				<div className="px-4 py-3 text-sm text-t-secondary">Updating...</div>
+			) : null}
+			{error ? (
+				<div className="px-4 py-3 text-sm text-red-400">
+					Error: {error.message}
+				</div>
+			) : null}
+			{data !== null && data !== undefined && !isLoading ? (
+				<div className="px-4 py-3 border-l-2 border-l-green-500">
+					<div className="text-xs text-green-400 mb-1">✓ Success</div>
+					<pre className="text-xs bg-t-50 p-2 rounded overflow-auto max-h-60">
+						{JSON.stringify(data, null, 2)}
+					</pre>
+				</div>
+			) : null}
+		</div>
+	);
+}
+
+function useSubscriptionUpdatePreview({
+	body,
+	enabled,
+}: {
+	body: SubscriptionUpdateV0Params | null;
+	enabled: boolean;
+}) {
+	const axiosInstance = useAxiosInstance();
+
+	// Debounce the body to avoid too many API calls
+	const [debouncedBody, setDebouncedBody] = useState(body);
+
+	useEffect(() => {
+		const timer = setTimeout(() => {
+			setDebouncedBody(body);
+		}, 300);
+		return () => clearTimeout(timer);
+	}, [body]);
+
+	const isDebouncing = JSON.stringify(body) !== JSON.stringify(debouncedBody);
+
+	const query = useQuery({
+		queryKey: [
+			"subscription-update-preview-test",
+			JSON.stringify(debouncedBody),
+		],
+		queryFn: async () => {
+			if (!debouncedBody) return null;
+			const response = await axiosInstance.post(
+				"/v1/subscriptions/preview/update",
+				debouncedBody,
+			);
+			return response.data;
+		},
+		enabled: enabled && !!debouncedBody,
+		retry: false,
+	});
+
+	return {
+		...query,
+		isLoading: query.isLoading || isDebouncing,
+	};
+}
+
+function useSubscriptionUpdate() {
+	const axiosInstance = useAxiosInstance();
+
+	return useMutation({
+		mutationFn: async (body: SubscriptionUpdateV0Params) => {
+			const response = await axiosInstance.post(
+				"/v1/subscriptions/update",
+				body,
+			);
+			return response.data;
+		},
+	});
+}
+
+function SheetContent({
+	cusProduct,
+	productV2,
+	customizedProduct,
+}: {
+	cusProduct: FullCusProduct;
+	productV2: ProductV2;
+	customizedProduct: FrontendProduct | undefined;
+}) {
+	const navigate = useNavigate();
+	const { customer, features } = useCusQuery();
+	const customerId = customer?.id ?? customer?.internal_id;
+	const entityId = cusProduct?.entity_id ?? undefined;
+
+	const product = customizedProduct?.id ? customizedProduct : productV2;
+	const { prepaidItems } = usePrepaidItems({ product });
+
+	// Get display info for custom items
+	const getItemDisplay = (item: ProductItem) => {
+		return getProductItemDisplay({
+			item,
+			features: (features as Feature[]) ?? [],
+			currency: "usd",
+		});
+	};
+
+	// Handle Edit Plan - navigates to plan editor
+	const handleEditPlan = () => {
+		if (!cusProduct || !customer) return;
+
+		const entity = (customer as FullCustomer).entities?.find(
+			(e: Entity) =>
+				e.internal_id === cusProduct.internal_entity_id ||
+				e.id === cusProduct.entity_id,
+		);
+
+		pushPage({
+			path: `/customers/${customer.id || customer.internal_id}/${cusProduct.product_id}`,
+			queryParams: {
+				id: cusProduct.id,
+				entity_id: entity ? entity.id || entity.internal_id : undefined,
+				version: String(cusProduct.product.version),
+			},
+			navigate,
+		});
+	};
+
+	// Get initial prepaid values from the current subscription
+	const initialPrepaidOptions = useMemo(() => {
+		return cusProduct.options.reduce(
+			(acc, option) => {
+				acc[option.feature_id] = option.quantity;
+				return acc;
+			},
+			{} as Record<string, number>,
+		);
+	}, [cusProduct.options]);
+
+	const [prepaidOptions, setPrepaidOptions] = useState<Record<string, number>>(
+		initialPrepaidOptions,
+	);
+
+	const handlePrepaidChange = (featureId: string, quantity: number) => {
+		setPrepaidOptions((prev) => ({
+			...prev,
+			[featureId]: quantity,
+		}));
+	};
+
+	// Build the request body
+	const requestBody = useMemo<SubscriptionUpdateV0Params | null>(() => {
+		if (!customerId) return null;
+
+		const body: SubscriptionUpdateV0Params = {
+			customer_id: customerId,
+			product_id: product?.id,
+			entity_id: entityId,
+			customer_product_id: cusProduct.id ?? cusProduct.internal_product_id,
+		};
+
+		// Add options if there are prepaid items with quantities set
+		if (prepaidItems.length > 0) {
+			const options = prepaidItems
+				.map((item) => {
+					const featureId = item.feature_id ?? item.feature?.internal_id ?? "";
+					const quantity = prepaidOptions[featureId];
+					if (quantity !== undefined && quantity !== null && featureId) {
+						return { feature_id: featureId, quantity };
+					}
+					return null;
+				})
+				.filter(Boolean);
+
+			if (options.length > 0) {
+				body.options = options as Array<{
+					feature_id: string;
+					quantity: number;
+				}>;
+			}
+		}
+
+		// Add custom items if we have a customized product
+		if (customizedProduct?.items) {
+			body.items = customizedProduct.items;
+		}
+
+		// Add free trial if we have a customized product with free trial
+		if (customizedProduct?.free_trial) {
+			body.free_trial = customizedProduct.free_trial;
+		}
+
+		return body;
+	}, [
+		customerId,
+		product?.id,
+		entityId,
+		cusProduct.id,
+		cusProduct.internal_product_id,
+		prepaidItems,
+		prepaidOptions,
+		customizedProduct?.items,
+		customizedProduct?.free_trial,
+	]);
+
+	// Preview query - fires when body changes
+	const previewQuery = useSubscriptionUpdatePreview({
+		body: requestBody,
+		enabled: !!requestBody,
+	});
+
+	// Update mutation
+	const updateMutation = useSubscriptionUpdate();
+
+	const handleConfirm = () => {
+		if (!requestBody) return;
+		updateMutation.mutate(requestBody);
+	};
+
+	return (
+		<div className="flex flex-col h-full">
+			<SheetHeader
+				title="Subscription Update Test"
+				description={`Testing update for ${cusProduct.product.name}`}
+			>
+				<IconButton
+					variant="primary"
+					onClick={handleEditPlan}
+					icon={<PencilSimple size={16} weight="duotone" />}
+				>
+					Edit Plan
+				</IconButton>
+			</SheetHeader>
+
+			<div className="flex-1 overflow-y-auto">
+				{/* Request Body Display */}
+				<div className="border-b border-border">
+					<div className="px-4 py-2 border-b border-border">
+						<h3 className="text-sm font-medium">Request Body</h3>
+					</div>
+					<div className="px-4 py-3 text-sm space-y-1">
+						<div>
+							<span className="text-t-secondary">customer_id: </span>
+							<code className="text-xs">{requestBody?.customer_id}</code>
+						</div>
+						<div>
+							<span className="text-t-secondary">product_id: </span>
+							<code className="text-xs">{requestBody?.product_id}</code>
+						</div>
+						{requestBody?.entity_id ? (
+							<div>
+								<span className="text-t-secondary">entity_id: </span>
+								<code className="text-xs">{requestBody.entity_id}</code>
+							</div>
+						) : null}
+						{requestBody?.options && requestBody.options.length > 0 ? (
+							<div>
+								<span className="text-t-secondary">options: </span>
+								<code className="text-xs">
+									{requestBody.options
+										.map((o) => `${o.feature_id}: ${o.quantity}`)
+										.join(", ")}
+								</code>
+							</div>
+						) : null}
+						{requestBody?.items && requestBody.items.length > 0 ? (
+							<div>
+								<span className="text-t-secondary">items: </span>
+								<div className="mt-1 pl-3 space-y-1">
+									{requestBody.items.map((item, index) => {
+										const display = getItemDisplay(item as ProductItem);
+										return (
+											<div
+												key={index}
+												className="text-xs border-l-2 border-l-purple-500 pl-2"
+											>
+												<span className="text-t-primary">
+													{display.primary_text}
+												</span>
+												{display.secondary_text ? (
+													<span className="text-t-secondary ml-1">
+														{display.secondary_text}
+													</span>
+												) : null}
+											</div>
+										);
+									})}
+								</div>
+							</div>
+						) : null}
+						{requestBody?.free_trial ? (
+							<div>
+								<span className="text-t-secondary">free_trial: </span>
+								<span className="text-xs">
+									<span className="text-green-400">
+										{requestBody.free_trial.length}{" "}
+										{requestBody.free_trial.duration}
+										{Number(requestBody.free_trial.length) > 1 ? "s" : ""}
+									</span>
+									<span className="text-t-secondary ml-2">
+										(card_required:{" "}
+										{requestBody.free_trial.card_required ? "true" : "false"})
+									</span>
+								</span>
+							</div>
+						) : null}
+						<details className="mt-2">
+							<summary className="text-xs cursor-pointer text-t-secondary hover:text-t-primary">
+								View raw JSON
+							</summary>
+							<pre className="text-xs bg-t-50 p-2 rounded mt-1 overflow-auto max-h-32">
+								{JSON.stringify(requestBody, null, 2)}
+							</pre>
+						</details>
+					</div>
+				</div>
+
+				{/* Prepaid Editor */}
+				<PrepaidEditor
+					prepaidItems={prepaidItems}
+					prepaidOptions={prepaidOptions}
+					onPrepaidChange={handlePrepaidChange}
+				/>
+
+				{/* Preview Result */}
+				<PreviewResult
+					data={previewQuery.data}
+					isLoading={previewQuery.isLoading}
+					error={previewQuery.error as Error | null}
+				/>
+
+				{/* Update Result */}
+				<UpdateResult
+					data={updateMutation.data}
+					isLoading={updateMutation.isPending}
+					error={updateMutation.error as Error | null}
+				/>
+			</div>
+
+			{/* Footer Actions */}
+			<div className="p-4 border-t flex gap-3">
+				<Button
+					variant="primary"
+					onClick={handleConfirm}
+					disabled={!requestBody || updateMutation.isPending}
+				>
+					{updateMutation.isPending ? "Updating..." : "Confirm Update"}
+				</Button>
+				<Button
+					variant="secondary"
+					onClick={() => previewQuery.refetch()}
+					disabled={!requestBody || previewQuery.isLoading}
+				>
+					Refresh Preview
+				</Button>
+			</div>
+		</div>
+	);
+}
+
+/**
+ * Main sheet component.
+ *
+ * To use this sheet, you need to:
+ * 1. Add "subscription-update-test" to the SheetType union in useSheetStore.ts
+ * 2. Add a case for it in CustomerSheets.tsx
+ * 3. Or, for quick testing, temporarily replace SubscriptionUpdateSheet import
+ *
+ * Example trigger:
+ * setSheet({
+ *   type: "subscription-update-test",
+ *   itemId: cusProduct.id,
+ *   data: { customizedProduct: product } // optional
+ * })
+ */
+export function SubscriptionUpdateTestSheet() {
+	const itemId = useSheetStore((s) => s.itemId);
+	const sheetData = useSheetStore((s) => s.data);
+
+	const { cusProduct, productV2 } = useSubscriptionById({ itemId });
+
+	const customizedProduct = sheetData?.customizedProduct as
+		| FrontendProduct
+		| undefined;
+
+	if (!cusProduct) {
+		return (
+			<div className="flex flex-col h-full">
+				<SheetHeader
+					title="Subscription Update Test"
+					description="Loading..."
+				/>
+				<div className="p-4 text-sm text-t-secondary">
+					No customer product found for itemId: {itemId}
+				</div>
+			</div>
+		);
+	}
+
+	if (!productV2) {
+		return (
+			<div className="flex flex-col h-full">
+				<SheetHeader
+					title="Subscription Update Test"
+					description="Loading product..."
+				/>
+			</div>
+		);
+	}
+
+	return (
+		<SheetContent
+			cusProduct={cusProduct}
+			productV2={productV2}
+			customizedProduct={customizedProduct}
+		/>
+	);
+}
diff --git a/vite/src/views/customers2/components/table/customer-products/CustomerProductsTable.tsx b/vite/src/views/customers2/components/table/customer-products/CustomerProductsTable.tsx
index 02de14ca1..901d0c54c 100644
--- a/vite/src/views/customers2/components/table/customer-products/CustomerProductsTable.tsx
+++ b/vite/src/views/customers2/components/table/customer-products/CustomerProductsTable.tsx
@@ -173,7 +173,7 @@ export function CustomerProductsTable() {
 
 	const handleRowClick = (cusProduct: FullCusProduct) => {
 		setSheet({
-			type: "subscription-detail",
+			type: "subscription-update-test", // SWAP: Change back to "subscription-detail" to revert
 			itemId: cusProduct.id,
 		});
 	};
diff --git a/vite/src/views/customers2/customer-plan/CustomerPlanEditorBar.tsx b/vite/src/views/customers2/customer-plan/CustomerPlanEditorBar.tsx
index 87bf3aea8..cb351f4c6 100644
--- a/vite/src/views/customers2/customer-plan/CustomerPlanEditorBar.tsx
+++ b/vite/src/views/customers2/customer-plan/CustomerPlanEditorBar.tsx
@@ -1,5 +1,4 @@
 import { parseAsInteger, parseAsString, useQueryStates } from "nuqs";
-import { useEffect } from "react";
 import { useNavigate } from "react-router";
 import { Button } from "@/components/v2/buttons/Button";
 import { ShortcutButton } from "@/components/v2/buttons/ShortcutButton";
@@ -60,7 +59,9 @@ export const CustomerPlanEditorBar = () => {
 		} else {
 			// We have a subscription ID, so we're editing an existing subscription
 			setSheet({
-				type: changesMade ? "subscription-update" : "subscription-detail",
+				type: changesMade
+					? "subscription-update-test"
+					: "subscription-update-test", // SWAP: Change back to "subscription-update" : "subscription-detail" to revert
 				itemId: queryStates.id,
 				data: changesMade ? { customizedProduct: product } : null,
 			});
diff --git a/vite/src/views/customers2/customer/CustomerSheets.tsx b/vite/src/views/customers2/customer/CustomerSheets.tsx
index eba5a9c59..2352c887b 100644
--- a/vite/src/views/customers2/customer/CustomerSheets.tsx
+++ b/vite/src/views/customers2/customer/CustomerSheets.tsx
@@ -11,6 +11,7 @@ import { BalanceEditSheet } from "../components/sheets/BalanceEditSheet";
 import { BalanceSelectionSheet } from "../components/sheets/BalanceSelectionSheet";
 import { SubscriptionDetailSheet } from "../components/sheets/SubscriptionDetailSheet";
 import { SubscriptionUpdateSheet } from "../components/sheets/SubscriptionUpdateSheet";
+import { SubscriptionUpdateTestSheet } from "../components/sheets/SubscriptionUpdateTestSheet"; // TEST: Remove this line to revert
 import { SHEET_ANIMATION } from "./customerAnimations";
 
 export function CustomerSheets() {
@@ -32,6 +33,8 @@ export function CustomerSheets() {
 				return <SubscriptionDetailSheet />;
 			case "subscription-update":
 				return <SubscriptionUpdateSheet />;
+			case "subscription-update-test": // TEST: Remove this case to revert
+				return <SubscriptionUpdateTestSheet />;
 			case "balance-selection":
 				return <BalanceSelectionSheet />;
 			case "balance-edit":