We had a paid chat app for social media celebrities/models to earn money chatting with their fans years back. Apple argued that despite a human being doing the work it 'took place in the app' so that makes it a 'digital service'. That means we had to accept IAP and of course pay them 30%. Made it impossible to to pay our influencers fairly.
Or you could have forced users to subscribe outside of the App Store on your own website.....