Whatsapp do not produce a Watch app. You only get notifications.
If the Watch app does not see your Watch check in "All Watches" top left of the app starting page.
If not...
First force restart the Watch
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, although it may seem irrelevant, Force Restart the paired iphone Force restart iPhone – Apple Support (UK)
If it is still misbehaving...
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 iphone are up to date. iOS16.2, OS 9.2
NB if your phone is iphone 7 or earlier do NOT update the watch to OS9 or you will need a new phone.
Update your Apple Watch - Apple Support
Update your iPhone or iPad - Apple Support
If you've completed that troubleshooting and the issue is still not resolved, Contact Support.
Click here > Contact - Official Apple Support
or phone numbers
Click here > Contact Apple for support and service - Apple Support