You can't actually sign up and pay for Spotify premium inside the iOS app, and I believe Netflix and Amazon Prime Video fall into a different "streaming video"

You can't actually sign up and pay for Spotify premium inside the iOS app, and I believe Netflix and Amazon Prime Video fall into a different "streaming video" category where they pay 15% instead of 30%, with some caveats: they must support both Airplay and AppleTV (exposing their entire video catalogues to Apple), and some other smaller things. It's all silly and arbitrary, and video game creators have been understandably upset for a long time.