Hello, I'm using the below extension to export the A-Leg Call-ID to the B-Leg. The A-Leg Call-ID is visible in the B-Leg INVITE as the header X-OCallID. <extension name="external_to_internal"> <condition field="destination_number" expression="(\d+)$"> <action application="set" data="hangup_after_bridge=false"/> <action application="set" data="continue_on_fail=true"/> <action application="export" data="sip_h_X-OCallID=${sip_call_id}" /> <action application="bridge" data="sofia/internal/${destination_number}@$${sip_proxy_ip}:$${sip_proxy_port}"/> </condition> </extension> Next to this, I also want to be able to append the Call-ID of the B-Leg to a custom header of the A-Leg. The B-Leg Call-ID would be appended to a response message, like 100, 200 or 4xx, 5xx, 6xx. Is this possible? If so, how? I took a look at using Lua hooks in lua.xml.conf, but I can't get the script to work.