Helping someone set up a new iPad today and I ran into a question: The only versions of QGC I can find in the Apple App Store are “QGC from TAJISOFT” and ALTA QGroundControl. I know ALTA is the Freefly version, but what is TAJISOFT? And none of these are the version I have on my iPad. I now see on the QGC website it notes iOS as “currently unavailable”, so does that mean all these versions are unsupported?
Error - not enough money paid to Apple
No, I was joking 
It could be something like not complying with some new app-store term, or almost anything.
It used to be an old MS Windows joke, that an error would indicate not enough money spent on hardware.
These days Apple want a cut of everything, even if you want to make it free.
Not sure that will get you very far at the moment. Best bet is to try on the Discord channel for an answer from a TBD maintainer.