The host or guest can allow mic access in Chrome by following instructions seen here:
Additional Privacy Settings
In addition to allowing mic access in the browser, it may also be necessary for the host or guest to go into the computer's privacy settings to allow mic access for Chrome or Firefox.
Instructions for Mac:
Choose Apple menu > System Preferences, click Security & Privacy, then click Privacy.
Select the checkbox next to Chrome or Firefox to allow it to access the microphone.
Instructions for Windows:
Go to Start > Settings > Privacy > Microphone.
Choose your preferred setting for Allow apps to access your microphone. (You will want to turn this on)
Under Choose which apps can access your microphone, turn the individual settings for apps On or Off. (If you see Chrome or Firefox in this list, you will want to turn mic access on here as well.)
If any settings changes are made outside of the browser, the browser will need to be refreshed or the computer rebooted for those new settings to take effect.