How to pair my Apple Watch?

Re: "How I pair my Apple Watch : I can’t pair Apple 9 series watch"

OK: re: compatibility

Wondering which WatchOS version is installed on the Watch

eg: watchOS 10 requires iPhone XS or later with iOS 17

and

whether the iPhone is still using iOS 16 or has been updated

and

whether or not the Watch has been paired with that phone ok before,

Eg: Set up and pair your Apple Watch with iPhone - Apple Support

or

Else: if is it a new phone to the Watch

Trouble-shooting:

See what to do: If you can't pair an Apple Watch with your iPhone - Apple Support