[Freeswitch-users] Call forward to another server/extension.

Dear all. I have an Opensips 3.0 + Fusion PBX setup. I would like calls received on Ext. 500 on Box A to be transferred to ext. 123 on Box B. I have successfully configured a trunk to Box B by setting up a Gateway and the status is REGED. I also added 123 in the Ext. field. In the dialplan expression I added 500. However, when I make the call it seems that I am transferred to ext. 500 on Box B and not Ext. 123. I am sure this has been discussed previously, but I can't seem to find much information. What am I doing incorrectly please?