Once you have added the device to Extreme Management Center, you will see the icon is orange.
Click on the Engine with the orange icon
Note that the Engine is not licensed.
Click on the update button under License
Accept the agreement.
In the below window to Update License, you may see Use Evaluation License, or Use Netsight Server license.
Once the license has been used from the server, it should appear to have valid license.
At this point, you should be able to enforce appliance, and then the device should be green.