---
title: "Attach Product"
openapi: "coreapi POST /attach"
---

{/* If payment is required, a Stripe `checkout_url` will be returned. If the customer's card is already on file, any upgrade or downgrade logic will be handled by default, and a `success: true` response will be returned. */}

<Tip>
  {" "}
  If the `customer_id` you send doesn't already exist, Autumn will automatically
  create a new customer. You can optionally set the properties of this new customer
  through the `customer_data` field.
</Tip>
