When it happens
- The callee reported the caller as spam.
What to check
- If you are the caller, check that your caller ID is correct and signed (STIR/SHAKEN), and that you are not calling people who opted out.
What the response looks like
SIP/2.0 607 Unwanted
Via: SIP/2.0/UDP 203.0.113.10:5060;branch=z9hG4bK776asdhds
From: <sip:101@pbx.example>;tag=1928301774
To: <sip:+15551234567@pbx.example>;tag=a6c85cf
Call-ID: a84b4c76e66710@203.0.113.10
CSeq: 2 INVITE
Content-Length: 0