Listening to 403 Forbidden Response

[micadeyeye@xxxxxxxxxxxxxxxx (Michael Adeyeye)]

Hi,
Please take a look at my code at  http://pastebin.mozilla.org/657836. At 
line 160, I want to execute a conditional statement when a response to 
sent SIP MESSAGE is 403/Forbidden. That is,

                if(status == 403){
                strcpy(sender, to->ptr);
                strcpy(sentURL, "Web session transfer blocked");
                }


How can I go about it? The current implementation does not work?

Thanks in advance.
Michael.