At the moment ED allows only to access a physical desktop if an X session is already running on that machine.

Even if the CreateDisplay key is enabled in the server configuration (server.cfg), the Enterprise Desktop doesn't create automatically a NoMachine display to let users connect to the desktop when no X server is running.

As a temporary workaround, it's possible to use the following manual procedure to create a virtual display:
https://www.nomachine.com/AR10K00710
How to use NoMachine 4 (free) on a headless Linux server