Things to check:
- Have you already provided microphone permission?
- On Chrome - click the lock icon in the URL bar
- On Firefox - there is usually a microphone icon
- Try on a different browser - Chrome and Firefox work best
- Do you have a microphone plugged in?
- A way to check this is open up another recording app and see if it is able to hear you
- Have you selected the right microphone?
- If you have more than one microphone available, make sure to select the one you the one you want