Apple watch 5 won't pair to iPhone 7 - iPhone out of Date

I am unable to pair my Apple Watch Series 5 running Watch OS 9 to my iPhone 7 running iOS 15.7

Both of them worked together in the past. But I'm unable to re-pair them. Pop up on the phone says "iPhone is out of Date, This apple watch requires a newer version of iOS"

There is no other solution offered other that now it is not compatible, though I used them together for years.

How can this be resolved?

Thank you