XG135 with APX320 - cant see the AP



i have an XG135.

Now i want to add some APX320 to the XG135.

I connected the AP to the management network.

In th management network is a DHCP Server.

The AP is getting an IP address, but is not shown in Outstanding APs.

So i am not able to activate the AP.

What is wrong? How can i see the AP as Outstanding AP?

Best reguards