SIP
439 First Hop Lacks Outbound Support
The first outbound proxy does not support the SIP outbound mechanism (RFC 5626) that the UA is trying to use.
이 코드를 보게 되는 경우
When a UA configured for SIP outbound connects to a proxy that doesn't support the outbound option-tag.
해결 방법
Upgrade the outbound proxy to support RFC 5626, or configure the UA to not require outbound support.