testing with this version:
``` [server:default] method = TLSv1.2+ verify_certificate = no require_certificate = no private_key = /etc/letsencrypt/live/abcsbc.com/privkey.pem certificate = /etc/letsencrypt/live/abcsbc.com/fullchain.pem ca_list = /etc/kamailio/ca_list.pem #ca_list = /etc/letsencrypt/live/abcsbc.com/cert.pem
[client:default] method = TLSv1.2+ verify_certificate = no require_certificate = no private_key = /etc/letsencrypt/live/abcsbc.com/privkey.pem certificate = /etc/letsencrypt/live/abcsbc.com/fullchain.pem ca_list = /etc/kamailio/ca_list.pem #ca_list = /etc/letsencrypt/live/abcsbc.com/cert.pem
```
in addition
``` event_route[tm:local-request] { # xinfo("Routing locally generated $rm to $ru\n"); if (is_method("OPTIONS") && $ru =~ "sip.pstnhub.microsoft.com") { append_hf("Contact: sip:DOMAIN:5061;transport=tls\r\n"); } } ```
OK?