Very interesting that they chose to go with a tipping model vs letting creators set up "pay to enter" chat rooms. That would be a lot more useful for the way I normally see the product used. I guess this was just the easiest lift from the technical side (not too much work beyond copy pasting some Stripe sample code). Although if it's just a matter of P2P money transfer for tips/donations then I'd rather use something…
I believe the only way around Apple requesting a cut of the payment is to explicitly avoid any notion of "unlocking" extras or access within the app. The tipping method is just a way for users to send money to each other, no biggie... but "unlocking a room" is basically an IAP, or could be defined as one.