Cannot get ANT+ & HR monitor to work on MAC

Hi my Elite Zumo pairs with my MAC book Pro from my Zwift rides but I want to monitor my HR so I bought an ANT+ plugged it into my MAC book Pro and nothing any Ideas please

What sort of HR monitor have you got?

Standard Garmin that came with my 920XT but I also Have a brand new one for swimming (Also Garmin)

I Got a reply from Doug that I read on Email but cannot find it here
really useful Thanks Doug!