Hello Mustiy,
Imagine that:
1. Every subscription has it's own user group.
2. People buy a a deposit of 600, they are placed in the subscription a user group.
3. Page / menu item available only to subscription a group becomes accessible.
4. User can access the page and download books. Each book on THAT PAGE ONLY costs $35.29, 17x = 599.93, books are downloaded.
Same goes for subscription B BUT we have 15 / 17 downloads there
We have all the links for the 17 books, but a book there costs: 38.66, therefore only 15 out of 17 books will be downloadable before deposit is spent.
Let me know if that's acceptable solution.
It requires: QuickSell Business only.
Cheers!