Subject. I heard that Apple forbids to make paid any built-in functionality. In particular, it’s not possible to subscribe or somehow demand money from people for receiving push notifications.
How about this from Google? Is it possible to provide such services for a fee? If Google doesn't care, does Firebase (as directly with the service providing the service) have such restrictions?
UPD: for iOS and Apple also did not find specific information (at least for comparison), so information is also welcome for this platform.