You're not a licensed money transmitter so you can't let users pay you for the purpose of sending money to someone else. Instead, you can provide a non-monetary good/service in exchange for money.

Then, it's your money to spend as you wish. You can spend it on rewards to great posters that you like and just so happen to align with the posts that your users provided paid feedback on.

Maybe this misses the point of Apple's restrictions, but could be a trusted way to enable you to pay great nostr users without needing a license.