Modifies an existing subscription or creates a preview of a modified subscription. You can add a coupon code, adjust the quantity of a subscription item, bill a customer in arrears for usage, replace one product with another product, change the product name, and even change the billing interval of a subscription (by exchanging the product). This endpoint also allows you to update the price of an item.
For more information, see Update Subscription Item. For XML examples and schemas, see the Additional Examples - Update Subscription Item.