---
title: "Attach"
openapi: "openapi POST /v1/billing.attach"
---

import { DynamicParamField } from "/components/dynamic-param-field.jsx";
import { DynamicResponseField } from "/components/dynamic-response-field.jsx";
import { DynamicResponseExample } from "/components/dynamic-response-example.jsx";

<Note>
  The attach endpoint subscribes a customer to a plan. It handles new subscriptions, upgrades, and downgrades automatically. For modifying an existing subscription (like changing quantities or canceling), use [update](/api-reference/billing/billingUpdate) instead.
</Note>

### Common Use Cases

<CodeGroup>

```typescript Subscribe to a plan
const response = await autumn.billing.attach({
  customerId: "cus_123",
  planId: "pro_plan"
});

if (response.paymentUrl) {
  // Redirect customer to checkout
  window.location.href = response.paymentUrl;
}
```

```typescript Custom pricing
const response = await autumn.billing.attach({
  customerId: "cus_123",
  planId: "enterprise_plan",
  customize: {
    price: {
      amount: 99900, // $999.00
      interval: "month"
    }
  }
});
```

```typescript Attach plan with prepaid quantities
const response = await autumn.billing.attach({
  customerId: "cus_123",
  planId: "team_plan",
  featureQuantities: [
    { featureId: "seats", quantity: 5 }
  ]
});
```

</CodeGroup>