Verify that a dropdown is available in the Device Portal of Edge IO's for Player resolution, and it works as expected WITHOUT a monitor attached to the Edge device.
We can support these resolutions:
1920x1080
1680x1050
1600x900
1024x1366
1536x864
1280x1024
1440x900
1366x768
1360x768
1280x800
834x1194
820x1180
834x1112
1280x720
810x1080
768x1024
1024x768
800x600