If users receive a 401 error when attempting to login to Zoom:
1.Clear cache
2. Manually enter URL http://zoom.us/signin
(The error is triggered if users go to http://zoom.us/Signin - note difference in capitalization. Apparently the incorrect URL now appears higher in Google searches)
Source: https://community.zoom.com/t5/Meetings/Error-code-401/td-p/10629