iPhone 13 bluetooth not pairing with iPhone 6s Plus bluetooth

Just got a new iPhone 13. I am attempting to pair its bluetooth with my iPhone 6 bluetooth.

Both devices see the other. But they won’t pair.

They both have the same updated 15.3 OS.

They are right next to each other.

I have already done the usual steps … turning bluetooth on each device off and on, rebooting both iPhones.

Assistance appreciated

Update … I unpaired my iPhone 6s Plus from my iPad 11 Pro … it had paired fine this afternoon, but once I updated to 15.3 OS, it no longer pairs with my iPad.