Does Apple take 30 percent commission on all purchase within an app using the In App Purchase API?
This isn't related to Apple Pay, though.
In-App Purchase remains the same, and it is a different API: https://developer.apple.com/in-app-purchase/
You cannot use Apple Pay to allow users to pay for any digital products, upgrades, etc. that are consumed within your app, you must use IAP where Apple takes a 30% cut.
Apple Pay is different and provides API to accept payments for physical goods and services. Apple does not take a cut from these transactions (that you're subject to), however you are paying around 2-3% in credit card fees per transaction, but that's common for accepting money anywhere.
Thanks for your answer.
I red the guidelines many times but it is still blury as that advices are sold through the app and a text advice can be considered as a digital content.
On your point of view you consider that the expert is external to the app so IAP does not apply, right?
Always struggled in between IAP and Apple Pay in our apps... it can be useful that Apple gives real world examples to illustrate their guidelines.