428
SIP
428 Use Identity Header
The server requires an Identity header to verify the caller's identity but it was not included in the request.
이 코드를 보게 되는 경우
In environments that enforce SIP Identity (RFC 4474) for caller authentication and spam prevention (STIR/SHAKEN).
해결 방법
Add a valid Identity header signed by an authentication service. Ensure your STIR/SHAKEN infrastructure is properly configured.