Cannot Answer Call Waiting on Zaptel

Ok here is the scenario.

Asterisk Server
Zaptel Dompatible Card X100

Call Comes in
Follows Inbound Call Rules and rings on Ring Group 0
Ring Group 0 ring on X2210 Which terminates on a Grandstream ht386 port 1.

Caller ID is selivered to Asterisk PBX.
Caller ID is passed on to HT 386
Caller ID Passes on to Handset and seen on display.

Call is answered all works fine.

While call is in progress another call comes in on same trunk.

How do i send a hook flash from the ht 386 to the trunk on the zaptel line?