If you are getting authorization errors when searching for contacts for trying to load the calendar this is normally a cookie and cache issue with the web browser you are using.
For Chrome: https://support.google.com/accounts/answer/32050?co=GENIE.Platform%3DDesktop&hl=en
For Firefox: https://support.mozilla.org/en-US/kb/clear-cookies-and-site-data-firefox
For Safari: https://support.apple.com/en-us/HT201265
For Edge: https://support.microsoft.com/en-us/microsoft-edge/delete-cookies-in-microsoft-edge-63947406-40ac-c3b8-57b9-2a946a29ae09
We do not support Internet Explorer anymore so move clients off that browser. We had to stop supporting it when Microsoft stop supporting it.