Imagine that you sell a $500 good both on App Store and Google Play and it includes both: unlocking in-app content AND some external content. For example, you teach coding and the $500 is a subscription in which you get premium educational content (more, better courses or the like) and a service such that you can contact with a tutor through Skype that will help you with your programs.
Suppose as well that $450 worth of value is the tutor's assistance and $50 worth of money is the digital in-app material the user gets.
In that case, would the fee apply? After all, those two are inseparable since it's simply buying more/better educational material/services.