I have downloaded ITSM sample space as test environment as I am evaluating Jira Service management (I am new to Jira). I didn't do any modification to the dowloaded template.
I have invited an agent (the mail adress of my Company) to join the service desk.
When I go to Project Setting -> People and I filter by role "Service Desk team" I can see my e-mail (I have a double role: service desk customer and service desk team).
When I try to assign an issue (ex. ITSAMPLE-2) I obtain the error message:

I went to Project settings -> Permissions -> Permission helper

I obtained this message:

Looking in the community answers, I found the suggestion
SETTINGS ->System -> Project roles

I can see the project role "Service Desk Team".
At this point I don't know how to proceed in my troubleshooting.
Any sggestion?
Thanks
Paolo