How to organize a subscription to a service with a web version in the app store?

Question

Apple App Store

We have a subscription application with a web version, and mobile versions of ios and android.
According to the appstore rules, you cannot use third-party payment acceptance systems other than the built-in one.
The question is, is it possible to write in the application about the possibility of paying in the web version (cheaper, no commission) or should the subscription cost be the same in the mobile and web applications?

Perhaps someone knows a link to the rules in the appstore documentation?
Thanks in advance for your reply)