CentOS - Mar 2020 - Pidgin + pidgin-sipe audo/video calls to Skype for Business

Has anyone got the audio/video call functionality to work with the 
CentOS 7 Pidgin packages? I primarily interested in Skype for 
Business/Office Communicator, but if you have anything else set up that 
supports audio/video, that may also be of interest.

I recently tried to join a "scheduled conference", and got a (working)
chat window, but didn't get any sound, and nobody else heard me. And 
there were no traces of video. I got an additional window with two 
sound-level bars, with a status line saying "Calling...", which seemed
to get no further.

I've tried "Test call" from the Accounts, with a similar result -
a new
window saying "Calling...", but no further progress.

I then went ahead and tried "Call a phone number...", again from 
Accounts, and entered my cell phone number. Then got the "Calling..." 
window again, and an actual call to the mobile phone. But when I 
answered it, nothing much happened. The Pidgin window was unchanged, 
i.e. there was nothing to indicate that the call had been connected, and 
I couldn't hear any sound at either end. Also, there was no call signal 
or anything in Pidgin before I picked up.

So, has anyone tried this functionality? Any luck? What's supposed to 
happen when I make a "Test call", anyway?

Thanks.

- Toralf