I was having the same problem with my series 6 watch, and was frustrated. I found these instructions on-line,"iPhone 15 Pro Max won't pair with my Apple Watch", and I am now paired.
Put watch on charger (needs to be 50% charged).
- With a web browser, go to: https://www.iCloud.com and sign in with your Apple ID. (I logged in with my computer). Open" Find My iPhone" and select "All Devices" (at the top). Then click your Apple Watch, select 'Erase Apple Watch', and select Next until the device is erased. Finally click "X" next to remove your Apple Watch. (My watch apps were saved in iCloud).
10.0.1 update started when that was finished.
After the update was done, the phone said that pairing was complete. The watch asked you to choose between downloading watch contents from iCloud, or starting from scratch.
My phone and watch are paired.
I hope that this will help.