The Zoom application needs to be open for you to receive chat messages and phone calls.  Follow these steps to allow Zoom to open automatically at log in:

1. Open System Preferences.
    
2. Open Users & Groups.  
   
    
3. Select “Login Items” at the top.  Click on “+” at the bottom.
   
4. Select Applications, Zoom.us.app then click Add.
   
5. Close the User & Groups window.  (Do NOT check Hide.)