When you join a call that has one or more conference rooms already connected, Highfive will automatically mute both your microphone and your speakers. We do this to avoid situations where computers in the conference room create screeching feedback loops.
If you are muted upon call entry, you will receive a notification that this has happened. To enable your mic and speakers, click on Unmute in the bottom UI area of the Highfive app.
If you don't notice a notification, but you find yourself unable to hear the remote participants, and they can't hear you, check to see if Unmute is an option, and if so - make yourself heard!