To confirm an event category has long description enabled:
  1. Go to onMessage > Content > Events.
  2. Click on the appropriate event category.
  3. Click Settings.
  4. Select "Show Long Description".
  5. Click Save & Close.
This will display any content that has been added to the Description box of the specific event.
Note: This will need to be done in the *primary* category that the event is published to. Enabling 'Long Description' in a category that the event is shared/published to -but is not the primary- will not provide you with the needed 'description' field in the event's settings.