### Description

Hello,

I'm trying to connect kamailio to Microsoft Teams. Dispatch is correctly configured and send SIP OPTION correctly. Following this tutorial : https://skalatan.de/en/blog/kamailio-sbc-teams, I added an Event_Route to add contact header to SIP OPTION from dispath to MS :

event_route[tm:local-request] { xlog("*** tm:local-request *** "); if(is_method("OPTIONS") && $ru =~ "pstnhub.microsoft.com") { xlog("L_INFO", "Append new contact !\n"); append_hf("Contact: sip:MY_SBC_NAME.COM:5061;transport=tls\r\n"); } xlog("L_INFO", "Sent out tm request: $mb\n"); }

When I check the log to see my sended frame, I don't see a contact header field : _INFO: <script>: Append new contact ! INFO: <script>: Sent out tm request : OPTIONS sip:sip.pstnhub.microsoft.com;transport=tls SIP/2.0 Via: SIP/2.0/TLS MY_SBC_NAME.COM:5061;branch=z9hG4bK4497.f3e5e754000000000000000000000000.0 To: sip:sip.pstnhub.microsoft.com;transport=tls From: sip:MY_SBC_NAME.COM.fr;tag=a76e006ace3802951ed860e08df964af-7971 CSeq: 10 OPTIONS Call-ID: 2e1278ea77796160-9837@MY_SBC_IP Max-Forwards: 70 Content-Length: 0 User-Agent: kamailio (5.2.1 (x86_64/linux))_

According the documentation about textop, append_hf(txt[, hdr]) : _This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE, FAILURE_ROUTE, BRANCH_ROUTE._

So my question is append HF can be used in Event_route ? Is there any other way to add contact header ?

Regards, Arnaud

### Troubleshooting

#### Reproduction

Can be easily reproducted with the following code (don t forget to set SBC NAME)

event_route[tm:local-request] { xlog("*** tm:local-request *** "); if(is_method("OPTIONS") && $ru =~ "pstnhub.microsoft.com") { xlog("L_INFO", "Append new contact !\n"); append_hf("Contact: sip:MY_SBC_NAME.COM:5061;transport=tls\r\n"); } xlog("L_INFO", "Sent out tm request: $mb\n"); }

#### Log Messages

INFO: <script>: Append new contact ! INFO: <script>: Sent out tm request : OPTIONS sip:sip.pstnhub.microsoft.com;transport=tls SIP/2.0 Via: SIP/2.0/TLS MY_SBC_NAME.COM:5061;branch=z9hG4bK4497.f3e5e754000000000000000000000000.0 To: sip:sip.pstnhub.microsoft.com;transport=tls From: sip:MY_SBC_NAME.COM.fr;tag=a76e006ace3802951ed860e08df964af-7971 CSeq: 10 OPTIONS Call-ID: 2e1278ea77796160-9837@MY_SBC_IP Max-Forwards: 70 Content-Length: 0 User-Agent: kamailio (5.2.1 (x86_64/linux)) ```

#### SIP Traffic

Traffic is in TLS, can't be easily readed.

### Additional Information

version: kamailio 5.3.9 (x86_64/linux) a5fd0a flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLACKLIST, HAVE_RESOLV_RES, TLS_PTHREAD_MUTEX_SHARED ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB poll method support: poll, epoll_lt, epoll_et, sigio_rt, select. id: a5fd0a compiled on 15:59:30 Jan 10 2022 with gcc 8.3.0

* **Operating System**:

No LSB modules are available. Distributor ID: Debian Description: Debian GNU/Linux 10 (buster) Release: 10 Codename: buster

Linux debian 4.19.0-17-amd64 #1 SMP Debian 4.19.194-3 (2021-07-18) x86_64 GNU/Linux