There is a point of sale system as part of the V4V App.
https://v4v.app/pos

It may not meet all of your requirements or your goals, but it certainly enables you to make a request for payment, and for the user to fulfil that request.

I wish I could have photography clients of mine pay in HIVE, but for that to happen I would a) need more clients and b) have them want to pay in hive.

Maybe if any of Hive account@mattclarke's kids gets hitched he can pay me in hive to capture their wedding :P (hint , hint)

Edit: and how horribly unkind of me to not CONGRATULATE you on finishing the book, in my original comment. That is a monumental exercise, regardless of length, genre, or target audience. Well done!