Fortiswitch isolated vlan no dhcp

Currently testing the isolated vlan setup on a standalone 248D.  If setting the interface to vlan 219 it works fine and gets dhcp from our server. If we do a vlan 219 with sub-vlan isolated of 220, no dhcp will work for this. Try dhcp snooping on and off and still nothing. Any docs on how to set this?

Thanks.