Watch not syncing with iPhone activity app.

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

The next steps would be to unpair and pair your watch again and restore from the backup:

Unpair and erase your Apple Watch - Apple Support

Set up your Apple Watch - Apple Support

Or try this;

Close the Activity app on the iPhone

On your watch: go the Home screen

(single press of the Digital Crown) and tap on

the Activity app icon (coloured rings).

Press firmly on the screen > tap on Change

your Move Goal > change the goal.

You can move the goal back once it's working again.

This little trick did the job, I had lost sync 2 weeks back for no unknown reason. Bumping the calorie count on a goal on the apple watch instantly applied to my activity screen on the iphone. Thanks.