Edit: The "dark" pattern is in the registration flow. It doesn't mention that the app requires a subscription anywhere until after you've created an account. Surely you could add a disclaimer before creating your account? This has nothing to do with the App Store.
Edit 2: I'm not saying you intended to implement a dark pattern. Just perhaps a UX oversight.
Edit 3: The download page would be another great place to put this info, since that's the primary CTA on the home page (there's 4 prominent download buttons).