[SR-Users] failure_route, change_reply_status, and append_hf: Not Working as Expected

Hello Kamailio Community, I'm currently working on a project that involves complex SIP routing and handling. I've encountered some difficulties while using change_reply_status, and append_hf functions in failure_route route in Kamailio. Although the documentation does provide guidance, the behaviors I am experiencing aren't aligning with the expected outcomes. Issue 1: failure_route I've set up a failure_route to handle specific SIP response codes (>4xx). However, I've observed that it get trigered and lunched, but I can't use change_reply_status or append_hf, I was using this first in onreply_route. Issue 2: change_reply_status I tried to use the change_reply_status function to modify the status of SIP replies, but it raises an error that this command cannot be executed here. Issue 3: append_hf I've also attempted to use append_hf in my failure_route block to add headers to replies, but the headers are not being added as expected. As a workaround, I've been using send_reply and append_to_reply for adding custom headers, and they seem to be working as expected. However, I found some old messages in kamailio mailing list, I can summerize what I learned like this ``` #Functions and Context - append_hf(): Adds a header to the currently processed SIP message. If you are in a route {...} block, then this adds the header to the request. If you are in an onreply_route, it adds the header to the reply. This function always acts on the message currently under scrutiny. - append_to_reply(): This function is used to add a header to a reply that will be generated by Kamailio at a later time. This function only affects replies generated by Kamailio itself and is not applicable for messages that are simply being forwarded. #Contexts - route {...}: This is typically where the incoming SIP request gets processed. Here, append_hf() will add headers to that request, and append_to_reply() will add headers to any replies that Kamailio might generate for this request. - onreply_route: This is where incoming SIP replies are processed. Here, append_hf() will act on the reply, not the request. ``` I'd like to know if there is a way to handle sip replies in failure_route, because send_reply make a new reply from kamailio, instead I want to keep some important headers from the original reply. I'd appreciate any insights or guidance the community can offer. Best regards,