Steam Link on AVP

Hi, I am trying to set up Steam Link on AVP and, whilst everything looks like it's ok, I end up with a blank/black screen with a spinning wheel in the bottom right and nothing happens, no matter how long I wait.

I have Steam installed on Mac Studio and it all looks like it connects ok, the Mac goes into full screen streaming mode, but absolutely nothing happens on the AVP - I've tried rebooting, reinstalling the apps etc and nothing has happened.

Every guide I've watched online just seems to work immediately so it's incredibly frustrating as I must be missing something really simple :(

Any help or guidance greatly appreciated. Thanks