Iphone XS

My experience is that it corrects itself after a few hours. I've also had issues with just "Activation Error" - and rebooted the phone a few times, I also signed in and out of my Apple ID. Nothing helped.

But after an hour I think, then it activated itself.

My advice, give it some time.

Okay, that's another matter. Then contact Apple Support directly.

https://getsupport.apple.com/