Iphone XS problem after ios 12.3.1 sw upgrade

Hello.

I guess that the only way is to update your iPhone in the recovery mode via iTunes.

1. Connect your iPhone to a computer, make sure that iTunes is updated to the latest version.
2. Press and release the volume up and then the volume down button and then press and hold the side button until you see a pop-up window on your computer that iTunes detected an iPhone in a recovery mode. If this didn't happen and your iPhone turned on, try again, iPhone's display should stay black.
3. You will be presented with two options: update or restore.
4. Click Update and follow the directions.

Hope it solves your issue. Please, come back with the results.

It's not solving the problem. My device keeps showing the message "Unable to activate. An update is required to activate your iPhone. Learn more at apple.com/UK/support. or SHUTDOWN.

Tried all the possible ways. Now don't know if it is a hardware issue or not. Anyone with any idea what to do?

See if this helps https://support.apple.com/en-us/HT201407

If the restore in the recovery mode doesn’t resolve your issue, I highly recommend to schedule an appointment or show up at the local Apple Store saying it’s an emergency, because it really is.