645 will not connect to my polar h10 or other hrm?

Hi guys.

I bought a hrm.about two years ago but for some reason it would not connect to my Garmin. I gave up trying and was annoyed because the Bluetooth was working fine on the HRM and watch connected to everything else i tried it with but not hrm.

Anyhow 2 years on and I really want to use a proper HRM reading..I bought a polar H10 two weeks ago and for the life of me I cannot get it to pick up the monitor???

I honestly don't know what I'm doing wrong?

As far as I can tell, the polar h10 doesn't have on/off button and works when electrodes are wet and belt is on. I'm seriously peed off now as I cannot understand why it won't pick it up?

I go to settings on watch, accessories and sensors. Add new and external heart rate 

It keeps saying "wear heart rate monitor to connect"

When naturally I have it on and moist before I hit search?

Can someone please help.woth this if possible?

Thankd