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.

https://developer.apple.com/in-app-purchase/In-App-Purchase-Guidelines.pdf

Happy to help in any way I can. I run a mobile-based startup myself.