1) Verify that the Zoom plugin is installed and activated.
Check Site Administration > Plugins > Activity Modules > Zoom
If you do not see Zoom, please submit a ticket and request the Zoom plugin be added to your site.
2) Ensure you have a Zoom "Pro" or "Business" account.
3) Review and follow items 9 - 14 in this doc: https://support.zoom.us/hc/en-us/articles/210865503-Configuring-REST-API-Plugin-with-Moodle
Official Moodle Plugin Page: https://moodle.org/plugins/mod_zoom