Never mind and thank you! I need to react since I can't see that red errors one more day. I'm going to delete the IAP from the App and Appstoreconnect for now and take care of it later. Thanks again

And this is the flow in Testflight starting directly from the settingsview:

Thank you for the Links. I couldn't find any new information that I did not already checked and confirmed in my post though. Here are the screenshots for the working purchase flow when I test it on my device when I run it locally. Hmmm…