One can’t, and wasn’t. If you read carefully, you may reconstruct the actual issue and the store policy: Either Proton mail removes mention of their premium s

One can’t, and wasn’t. If you read carefully, you may reconstruct the actual issue and the store policy: Either Proton mail removes mention of their premium service from the app (and the app can still provide this service to anyone paying outside of App Store) or they keep it and then provide in-app purchases. They clearly decided to use IAPs. If you ask me, this is a smart move, as many customers won’t be bothering with other payment options.