post https://rest.cleverbridge.com/subscription/updatesubscriptionitem
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 XML examples and schemas, see the Additional Examples - Update Subscription Item.