This is getting ridiculous:
- even the (hopefully functional) injection of a new IMEI and Serial Number with XPrivacy has not solved the issue
- installation of the free version worked, and it would start correctly multiple times, for ONE day. The following day I got the same 'An error has occurred' message...WTF?

I am now considering the cumbersome 'carefree package' method offered elsewhere. It is so complex and error prone that I really wanted to avoid it, yet what else could I possibly try? If even the official version downloaded from the Playstore is failing on day #2, this hack will probably fail as well.

The very last attempt is to use a brandnew SIM card, create a new Google identity with it, and then install the app once more.
I have no clue what this weird app is trying to verify and why it fails utterly for me, regardless what version I am trying to run.