[stickydink]

Apple guidelines, section 3.1.1, regarding in-app purchases:

>Apps may use in-app purchase currencies to enable customers to “tip” the developer or digital content providers in the app.

Section 3.1.2(d), regarding permissible use of other payment methods:

>3.1.3(d) Person-to-Person Services: If your app enables the purchase of realtime person-to-person services between two individuals (for example tutoring students, medical consultations, real estate tours, or fitness training), you may use purchase methods other than in-app purchase to collect those payments. One-to-few and one-to-many realtime services must use in-app purchase.

https://developer.apple.com/app-store/review/guidelines/

It's fuzzy, perhaps, given the word "may". Apple's unofficial advice for fuzzy guideline questions is to implement, submit, and argue your case once it's live.

[PeterisP]

It's not fuzzy - 3.1.3 says that may not use "purchase methods other than in-app purchase" (since it's not one-to-one person-to-person service but tipping for one-to-many content) and must use in-app purchase.