[Freeswitch-users] issue with disposition cause overriding

i am trying to override specific disposition cause coming from leg B and sending the modified cause to leg A using, https://freeswitch.org/confluence/display/FREESWITCH/Cause+Code+Substitution... the lua file returns sip_invite_failure_status variable as '-ERR No such channel!' and not the code 480 However, from sip trace i can see '480 temporary unavailable' from leg B and because of that my lua script which i am calling before bridge application is not able to override the cause from 480 to 503 What i am missing?