[David_FF]

Maybe I missed it

But how will they actually know how much money developers are making via external web purchasing? Audits?

In my opinion working with both Apple and Google's billing libraries is pretty painful. Many developers use third parties to make it easier like Qonversion or RevenueCat. These all have to go through Apple and Google respectively

If you can just have a web page to do it, that seems easier actually. You can just save if the user is paid or not directly in your backend after they make a purchase

[semiquaver]

  > Developers are required to provide a periodic accounting of qualifying out-of-app purchases, and Apple has a right to audit developers' accounting to ensure compliance with their commission obligations and to charge interest and offset payments.