[Users] purposely dropping reply message

Hello, How/Where would be the best place to purposely drop a particular reply message ( > 400 ) I have armed both the reply route and failure route and attempted to drop the message by calling the drop() function but this doesn't seem to work. Is there a simple method for conditionally dropping a reply message? My goal is to force the UAC that created the original request to retransmit (UDP) the request in certain scenarios, such as when ACK to an initial invite has not been fully processed by the downstream UAS but a re-invite has been received by the UAS causing the UAS to return a 400 for the re-invite. I do not want the UAC to see the 400 reply, instead I simply want the UAC to resend the re-invite because no final response has been received, presumably by this time the ACK processing will be finished and the retransmitted re-invite would be handled smoothly. I realize replies are routed based on via headers. Is there some way to short circuit this routing other than drop()? Thanks Tim Tried this from failure route if(t_check_status("400")) { xlog( "L_ERR", "400 message in failure route 2 ********** \n" ); drop(); return; } Tried this from reply route if(status == "400") { xlog( "L_ERR", "400 in reply route 2 .... dropping\n" ); drop(); return; }