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.
Когда вы видите этот код
In environments that enforce SIP Identity (RFC 4474) for caller authentication and spam prevention (STIR/SHAKEN).
Как исправить
Add a valid Identity header signed by an authentication service. Ensure your STIR/SHAKEN infrastructure is properly configured.