Follow these steps:
- Does your guest have the correct mic selected in their Cam/Mic settings?
- If you're on a computer, it's possible you have the wrong speaker selected. Trying clicking the "Test speaker" button in your audio settings. If you don't hear a noise, try switching to a different speaker.
- If you're on an iPhone or iPad, you may be experiencing a rare Safari bug. Try tapping on the video of the person your can't hear. A menu should appear that helps you fix the issue.