@th3j35t3r it seems the mobile interface can be problematic if the screen doesn't auto-rotate. In Portrait mode you can't see the drop down for acknowledging the permission issues that seem to pop up by default. Once I ack'd the errors it put me in the conference and I could activate the mic/cam.
@th3j35t3r Further for users in portrait mode the toggle button for the gallery view over/underlies the Hang Up... so use caution if you're locked into portrait.
@th3j35t3r Dug in and found that my Tusky app wasn't running the #COSOcall on mobile - the default browser was called. Had to go into those permissions outside the call and find and enable them. The permission splash didn't work on my device (Android) at call opening, but I found it was blocked in Apps > Settings > Chrome and now it works fine. Auto-rotate on the screen works fine for me but another user (iPhone) reported it didn't for her.