Fortigate+Fortiswitch+FortiAP

Hi

So we had a test AP setup in Fortigate under a physical interface with a guest and a staff WIFI setup - all worked correctly and correct DHCP IP assigned.

I have since connected a Fortiswitch, i have created a new VLAN and took the IP address and range from the existing physical guest VLAN and used that on the new fortiswitch VLAN (then changed the address on the physical)

the AP is up + online, I can see both SSID's, but when I attempt to connect to the guest WIFI I get a random IP address on the wrong subnet an the device never connects.....log states 'Wireless station DHCP process failed with no server response' 

I have adjusted all policies to allow traffic as far as I can see.

Any ideas?

Thanks.