ondraayyy Hi! Finally managed to check all the things on your list. Hell Apple likes to make things difficult. Nevertheless my app works with TestFlight, hurray. The original error message disappeared, however scirra IAP still doesn't seem to work.
I have checked all the things on your list, besides that I tried to turn on/off test mode in the IAP object. I have an event if the store listing failed/successed It should set visible an error/success message (simple text objects), but nothing happens.
Maybe I have to send my App to beta review or something?
Thanks!