We got 3 gateway in system.
2 of them are old type which can only configure them from GCE.
The new one (4 port gateway) which can configure by press button on box.
But I can not configure this one by GCE nor NET3 form GIO@5.
Have you checked if there is an update for concert? Current version is 4.0.2.
Not 100% sure, but I don't think there are Net3 gateways that can be controlled by GCE but not by Concert.
As Ueli say, you need Concert for that. GCE is the old, discontinued, setup program.
if you do not have it on your @5 you will find it here. https://www.etcconnect.com/Products/Networking/Software/Concert.aspx