Gruop Facetime

I have an imac 2015 running MacOs High Sierra

My facetime works fine one to one face calls.

The problem is there is no option to start or add someone into a call to make it a group call.

I have an ipadand iphone for which this isn't a problem but the layout looks different to my mac.

I've looked into all the other common threads but the problem seems to be that the facetime app on my mac is older/different to that on my other devices

Any help greatly appreciated