App Inventor 2 does not support revenue earning or payment transactions.
Thunkable is a commercial Block compiler designed for commercial activity. It appears you should consider using a compiler that has built in payment features. App Inventor is designed for educational purposes, not commercial endeavors although some developers use AI2 that way.
One tool available for AI2 is an extension for AI2 is App Inventor Extensions: Billing | Pura Vida Apps that you might be interested in.
See this post to understand why you can not do this with App Inventor How can I add admob or any monetize extension to my app via app inventor only please?
Regards,
Steve