I am building an app for a client that will have 30 days of content for free, thereafter you are required to buy a subscription via in app store purchases.
However,
The guidelines mention this is only allowed for specific types of content:
11.9 Apps containing content or services that expire after a limited time will be rejected, except for specific approved content (e.g. films, television programs, music, books)
11.15 Apps may only use auto-renewing subscriptions for periodicals (newspapers, magazines), business Apps (enterprise, productivity, professional creative, cloud storage), and media Apps (video, audio, voice), or the App will be rejected