I've seen this issue a lot but can't see a solution.
I can't log onto the BT Sport via Safari or Firefox on the Mac.
Using Firefox It displays a message 'An error Occurred , Sorry - we can't play this at the moment'.
This has been ongoing for a few weeks. It has never worked.
Works on the iPhone but not on the Mac.
I have never used a mac but on my windows laptop the solution was to download the virgin tv go app from the windows store. since then it has worked really well. so if the virgin tv go app is available in the mac app store you could try that.