I am planning to sell digital products using for dollar value that gives end users redeem codes. This redeem code will be used by the end-user on an external website to claim the product.
In terms of technical implementation, I am trying to validate if this is possible to make an API call after a successful payment. The API call with include a list of purchased items with an identifier and receive a response with a list of redeem codes. After I get the redeem codes, I want to display the Thank you page and all the redeem codes on it. At the same time, I also want to update the order with this codes in Shopify so that I have history of orders and redeem codes tied to it. These codes will be generated on the fly by the external system using an API call.
From what I have researched so far, I can leverage webhooks (order create) and update the order with redeem codes using my own custom logic but that still doesn't give me the ability to show the redeem code on Thank you page. I also plan to use Shopify Plus and looking at the option to modify the checkout template, there isn't anything particular I can use to tap in between successful payment and Thank you message.
I created a custom app to explore the possibilities of using API but found that I don't have access to Checkout API.