I am using the api_hangup_hook variable to let my internal system know when a call is terminated.

Every now and then  my calling party cancels the SIP Invite before my dial plan is finished.  IN this case FreeSWITCH properly responds with a "487 Request Terminated"  

However, this does not fire the command assigned to the api_hangup_hook variable.  This is probably also proper since the call has not yet been established.  

My question is whether there is a place somewhere where I can hook into the processing of the CANCEL SIP message.

Thank you

Oleg