Setup your data as follows:
User
api_key: text
Call that API key in your backend workflow (current user’s api_key).
Use the success response from Stripe to DO SOMETHING after the message (if failed, take user back somewhere, if success, change the users role) type of thing.
EDIT:
You’ll want to start from the very basic stuff, to the more advanced stuff to precisely nail down what you’re trying to do. There are a lot of different types of logic you need to setup for this type of system.
This is a good site as an example. Doesn’t explain data, but it kind of shows the operation.