You need to select Manage under In-app Purchases section in your App Store connect account. You can also check out our service Qonversion.io, if you don't want to build your own server to validate the receipts.

Provide an onboarding experience on mobile web and offer a subscription with Stripe there. Once a user subscribed, send the link to download the app, he needs to log in with same credentials as on web. Then you provide premium access based on his Stripe subscription. This is not going against any Apple's policies. You do need backend logic to handle authentication and subscriptions. You can check our solution for that here https://documentation.qonversion.io/docs/stripe-integration