I'm trying to determine how services such as park mobile avoid the 30% transaction fee that apple imposes. Is it because parking is a physical good? Thanks!
Apple specifically precludes anything that can't be delivered via the app from using in-app purchases. So you're free to tie a credit-card to services and real-world fees (think Uber) without paying Apple any transaction fees.
Here's Apple's documentation on what they support (and don't allow) for in-app purchases.
Happy to help in any way I can. I run a mobile-based startup myself.