Soundbuds Curve, Windows, Hands free mode

I have a new pair of Soundbuds Curve (BT5.0) - I can pair them fine with my Windows PC but get no audio in Hands-free mode with zoom or skype (or even selecting headset as audio output). The microphone works, and from the PC side things look good (connected as a handset, testing shows the PC thinks it’s outputting sound), but nothing comes through the headset. Playing music via headphones (as opposed to headset) mode works fine. I get bi-directional communication using zoom on an S9 or iPad (6th gen), so it’s something related to the PC. This happens on two PCs (intel 7260 and 8265 wireless chipsets). I’ve updated all of the drivers etc. that I could find, but still can’t get sound in hands free mode. These are the only bluetooth headset I have (speakers work from the PC), so I haven’t been able to test other handsfree devices. Any ideas? thx