Here's how to fix it:
The person whose microphone is muted should click the Change Camera & Mic button (the gear icon) at the top of their video.

Once they click on that, they'll see a popup where they can select and confirm their video and microphone inputs.

If both the camera and mic are correct and the mic is responsive, click save and the video feed will be refreshed with the new audio input. The mic now should be unmuted and functioning properly.
What causes this to happen?
This is usually caused when a person disconnects and/or connects microphone/headphones while on-screen.
Have questions or suggestions? Email us at [email protected]. Happy Crowdcasting! 🎥