That's not Apple Pay, these are iOS in-app purchases. If you or the author call it that, nobody here will understand you.
To be fair, as a user, I don't see the expression "in-app purchases" while I _do_ see the Apple Pay logo. It's easy to get them confused.
So it's not entirely incorrect (but definitely confusing) to say that the end user is "paying using Apple Pay", but they're paying Apple, not the app vendor.