You may recognize that Issue Forms for Confluence does not support the customer portal configuration of the project type "Service Desk". You can use the "Issue Form - create form", if you follow the Step-by-step guide.
Step-by-step guide
Change the Permission Scheme (must be done by a Jira Administrator)
Grant the Permission "Crate Issue" to "Application role - Any logged in User"
Grant the Permission "Browse Projects" to "Reporter"
Change the Screens (only required for version < 2.1.0 and must be done by a Jira Administrator)
Remove the Field "Request participants" from the issue create screens of the project.
Now you can use the "Issue Forms - create form" and the form will be shown to all users who have the permission to login into Jira.
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