A possible workaround that has worked for me and others has already been posted.
Do you have a DHCP server running on the same network? If you don't, try adding one. It seems the AP grabs additional IPs from DHCP aside from the management IP you assign during provisioning.
I had the same issue, 2802i, 18.104.22.168.
At first I didn't have a dhcp server on the network. Solved that by using TFTPD64 as dhcp server.
My other problem was, when configuring the Controller IP settings, i entered a non existing default gateway.
If the controller interface is unable to ping its configured default gateway, the controller interface won't come up.
So, the solution for me was to enter an ip-address that could respond to ping as default gateway for the controller, during the setup wizard for Mobility Express. Also make sure you have an existing dhcp server that can hand out ip addresses for the AP.
1. Change AP mode to capwap,,,, (press esc button when the AP is booting and change the mode to CAPWAP).....
2. Add the mac addresses of APs to allow list on WLC security policy.
if above two step does not resolve the issue then apply the third step as well in addition to 1 and 2.
3. configure the port as a trunk on switch where the AP is connected. and make native vlan that port which you want to AP should be. (i-e if you want the APs to get the IP address from vlan 20 so you will need to make vlan 20 as a native on that port)..
These steps resolved my issue.