How to add approvers and articipants to request as a JSD customer?

There are APIs to fetch customers connected to a project but as far as I can see they only work if you are at least a JSD agent and I’m trying to do it for my customers as well.

I have tried to give the customers connected to a service desk permission using the following option in Custom permission:

  • Any customer or organization, by searching this project. This option allows them to search all customers in the current project.

To me it sounds like that should make it work, but it doesn’t. If you are not adding your request from the default Atlassian page that is.

The API I’m trying to use is:

/rest/servicedeskapi/servicedesk/{serviceDeskId}/customer

Does anyone know of another API to fetch this information or if there is some other permission I have to set to make it work?