It's possible that: 1) The host did not have their audio un-muted... The host can unmute their audio by right-clicking on their name (in the user-list) and selecting Unmute. 2) Push-To-Talk (a bit like a walkie-talkie) is enabled... By default, Push-To-Talk could be enabled for your Nefsis meeting. Try pressing (and holding down) the "Push-To-Talk" button at the top of the user-list while speaking. In either case, you should see the person's name in the user-list highlight green when their talking. Hope this helps.