iOS payment apps: does Apple charge 30% of transacted amount?
From what I understand, Apple says

3.1.5 Physical Goods and Services Outside of the App:
If your app enables people to purchase goods or services that will be consumed outside of the app, you must use purchase methods other than in-app purchase to collect those payments, such as Apple Pay or traditional credit card entry. Apps may facilitate transmission of approved virtual currencies (e.g. Bitcoin, DogeCoin) provided that they do so in compliance with all state and federal laws for the territories in which the app functions.