reminders

First check that Reminders are accessible on the iPhone.

Assuming they are...

First force restart it

i.e. 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.

Then while it is restarting, Force Restart the paired iphone   Force restart iPhone – Apple Support (UK)

If that is no help

 Unpair and erase your Apple Watch

and then

Set up your Apple Watch

 If no better you may want to unpair then set up without restoring the backup.

You may also want to make sure the software on the watch and the iPhone are up to date. i.e. OS9.2 and iOS16.2

If you've completed that troubleshooting and the issue is still not resolved then Contact Support.

Click here > Contact - Official Apple Support

or phone numbers 

Click here > Contact Apple for support and service - Apple Support

Thats great, glad I could help.