cal.pub0.org

Create a Webex acount, if you don't already have one.
Go to Webex for Developers and sign into to your Webex account. (Note: If you're creating a new account, create it on Webex, not on Webex for Developers)
On the upper right, click the profile icon and go to "My Webex Apps"
Click on "Create a New App" and select "Integration"
Choose "No" for "Will this use a mobile SDK?"
Give your app a name.
Upload an icon or choose one of the default icons.
Give your app a short description.
Set the Redirect URI as <Cal.com URL>/api/integrations/webex/callback replacing Cal.com URL with the URI at which your application runs.
Select the following scopes: "meeting:schedules_read", "meeting:schedules_write".
Click "Add Integration".
Copy the Client ID and Client Secret and add these while enabling the app through Settings -> Admin -> Apps interface