Don’t know why my Apple Watch is not functioning anymore

The first (and simplest) thing to try if something isn’t working right is to restart your Apple Watch and its paired iPhone. If necessary (device not responding), try a forced restart. Both methods can be found here:

How to restart your Apple Watch - Apple Support

Restart your iPhone - Apple Support

If that doesn't help, the next steps would be to unpair and pair your watch again and restore from the backup just created. This should result in no loss of data. It deletes all temp and corrupted files and re-indexes the file system.

Unpair and erase your Apple Watch - Apple Support

Set up your Apple Watch - Apple Support

Also see:

If your Apple Watch won't charge or it won't turn on - Apple Support

There are 2 things that fix about 98% of watch problems;

1.Force restart

Press and hold both the side button and Digital Crown for at least 10 seconds, then release both buttons when you see the Apple logo.

This fixes a surprising number of issues.

2.Unpair and re-pair and setup as new.

This returns the watch to the way it was when you bought it brand new.

You can Unpair and re-pair and restore the watch from a backup but the problem with this is that whatever software glitch you had could be reintroduced from the backup you made when the watch was faulty,therefore leaving you no further forward.