GS724T - can't get VLANs to work over LAG connected to Fortigate

Greetings,

I have a GS724Tv4 that I can't get VLANs to work for using a LAG interface to a Fortigate firewall and am looking for assistance.

• The GS724T has ports 23-24 configured as LACP and the Fortigate has ports 2-3 configured as an 802.3ad aggregate.
• I have two ethernet cables connecting ports 23-24 of the switch to ports 2-3 on the Fortigate.
• The LAG interface on the GS724T shows that the link is up.
• I have a VLAN-204 with DHCP running on the Fortigate LAG at 192.168.2.65.
• I have a VLAN-204 set up on the switch with ports 7-9 marked as untagged members and the LAG marked as a tagged member.
• I have a PC plugged into port 9 with an IP address of 192.168.2.67 but I cannot ping the Fortigate 192.168.2.65 address.

It appears that the switch is not passing traffic from port 9 to the LAG interface.

I see nothing wrong with the configuration and have reviewed the manual several times. 

Can anyone give me any ideas of what I may have missed or how to troubleshoot this?

Thanks