What's is the prablom

First 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, unless your provider forbids it,  reset the router to factory settings which usually involves a paperclip on a little hole. 

Try again to pair the Watch. 

If still problems I recommend reviewing the steps in the articles below 

If you see 'Unable to Verify Update' when updating Apple Watch - Apple Support

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