Let me explain the reason of this …. situation.
In Server/onPremise version of Jira Service Desk, you have to grant users access to right application. So Go to Cog menù –> Application –> Application access and you see this form:
where Jira Administrator set who can access to Jira service Desk.
Wooow, and for Cloud instance?
For Cloud instance exists the same but, as you understand, cloud have different configuration and situation. You have to see User Management section to see the same form
Of course, I’ve removed the email and various information of my Cloud instance, but if you see your cloud instance, you see similar view.