Start by reading this article
If you see “Unable to Verify Update” when updating Apple Watch – Apple Support (UK)
Also check you have no other sports watches like Fitbit that are paired to your iPhone
Then 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 while the watch is restarting Force Restart the iphone
Force restart iPhone - Apple Support
Then in the iphone, Settings, General, Transfer or reset iphone, Reset, Reset network settings.
Then reconnect the iPhone to Wi-Fi.
Make sure you have no VPN or VPN based adblocker in the iphone in Settings, General, VPN & Device Management.
Then, if you have a home router, tun it off and turn it on again.
Try again to pair the Watch.
If still unsolved I recommend reviewing the steps in the articles below
How to pair your Apple Watch with a new iPhone - Apple Support
If you can't pair an Apple Watch with your iPhone - Apple Support
If your Apple Watch isn't connected or paired with your iPhone - Apple Support