The Zoom Google Add-on* occasionally needs to be reauthorized. To do so, sign out of the Google Zoom Add-on and back in and re-authorize, reading the prompts for any new authorizations. 

*The Google Add-on add Zoom links to meeting using the Add video conferencing > ADD-ONs > Zoom Meeting button (the Make it a Zoom Meeting button in Google Calendar in Chrome uses the Zoom Chrome Extension)

Video Demo

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Sign out of Zoom Add on and Back in

1. Open Google Calendar, click the Zoom icon in the right side-bar (if you don't see the Zoom icon, click < in the bottom right to show the right sidebar)
2. Click the three dots near the top right.
3. Click Sign Out
   
4. Click Sign in
   
5. If prompted to re-authorize read through the access and check the box for Allow this app to use my shared access permissions (this is required if you schedule meetings someone else is the Zoom Host of through Zoom schedule privilege). Then, click Authorize.
   
6. Schedule a Zoom meeting in Calendar; if you have issues, clear your browser cache and try scheduling again.