Hmm. I’ve had times where it took 15 or 20 goes using Configurator 2 - Apple’s slightly more pro interfacing software that does the same in your instance and throws the same error messages and tantrums.
assuming given the lengths you’ve gone to you’ve tried a different network /internet connection, tried in safe mode etc etc
i really think both you and Daniel will find a quick fix with a genius appointment. Not that you e done anything wrong it sounds like you’ve followed the procedure to the letter. But the restore process is, well almost sentiently stubborn much of the time (most likely erring on the side of security which is no bad thing), but the one time I couldn’t get a restore working with that code Apple sorted it quickly in the store - and at no charge to me at least so I wouldn’t panic.
so do let us know how you get on but I have faith you’ll both get sorted :)