Hi,
It is ecause there is no VLAN mapped to VAP profile. if we do not map any VLAN to the VAP, clients will get IP from the AP subnet and mapped to the AP VLAN.
Here is the work arround,
Clear a VLAN ( Ex ;VLAN 99 ) for Client and apply an IP address to that VLAN interface (VLAN 99) ( don't forget to use "operstae up" command ).
Now create a DHCP pool with the same subnet as the VLAN interface (VLAN 99) created for the client.
Now map the CLient VLAN (VLAN 99) to the VAP profile.
Please ensure that the forwarding mode is Tunnel mode :)
For your ref :