This solution was provided by Sait Kiremit. It has earned a $50 donation to FIRST by Blended Perspectives.
In Jira Service Desk, a customer request type needs either a custom field or an attachment. For example, if the user does not enter the value in the custom field called "Request Participants" on the request screen, the user will be warned of a required attachment. If the user enters the "Request Participants" field, this warning will disappear when creating a request.