thanks @Alex T⚜️

I've tried telling Apple support that I'm not going to use the app to charge users, only my webiste:

"well, I removed all membership informations from my website. Now users can't buy anything additional. Neither they can view information about additional memberships. Please let me know if it works now"

this is their reply:

We noticed that your app includes or accesses paid digital content, services, or functionality by means other than in-app purchase, which is not appropriate for the App Store. Specifically:

- The premium memberships can be purchased in the app using payment mechanisms other than in-app purchase.

Next Steps

The paid digital content, services, or subscriptions included in or accessed by your app must be available for purchase using in-app purchase.

Apps that offer paid digital services and content across multiple platforms may allow customers to access the content they acquired outside the app as long as it is also available for purchase using in-app purchase. See Guideline 3.1.3(b) Multiplatform Services for more information.

If you have any additional information to provide regarding the digital content and services in your app and how the guidelines apply to them, please reply to this message in Resolution Center and let us know. If there is information you'd like us to consider in our review of future submissions, please feel free to include it in the App Review Information section of App Store Connect.

Resources

- See how to implement in-app purchase with the StoreKit framework.

- Review step-by-step instructions for creating in-app purchases in App Store Connect.

- Learn more about our policies for apps that offer paid digital content and services.