AirPods Pro aren't connecting to new iPhone

I bought 2 AirPod Pros (2nd Gen). I kept one pair and gave the second pair to someone else.

The second pair can’t be seen in Find My.

But if I connect to them they do appear under my devices

We have removed them from both iPhones and have done a factory reset on them (open case and press the back button for 15 seconds) but they still don’t appear on the second iPhone

any ideas?

Thanks

[Re-Titled by Moderator]