Wow...I think you just discovered a hole in Apple's draconian app store policies. They don't let you link to your website from your app if the site has a way to buy a subscription without paying the Apple tax. But what if you sell ad space in your app through an intermediary, and then turn around and bid on ads for users that have your app installed? You might be able to get them to notice you and sign up on the web instead of through the app.

Genius.

(I'm only being half-facetious)