Hey vs Apple. How to avoid In-app payments?

So the 1.0 version of the Mindwave.app got rejected last night.

"We noticed that your app offers a subscription with a mechanism other than the in-app purchase API."

Which seems to be the same issue Hey is having with their rejection:

Should I wait and see what happens with Hey and the EU investigation? Should I just proceed and ad the In-app purchases?

FYI: In my case, the Mobiel App is only 25% of the web app experience (and subscription).

What would you do? And If you experienced the same rejection, how did you handle it?