Problem: Requester's is unable to get Zoom to user computer's mic and video on a Mac.

Solution: Requester should be sure the computer OS is up-to-date with the latest security patch for their OS and that the Zoom desktop client is up-to-date as well.  

Allow Zoom to access your mic and video. 

You would want to open System Preferences > Privacy & Security > Under the Microphone and Camera categories, allow Zoom to access these by checking the boxes on.