Locate the response family
- 1xx ProvisionalRequest is progressing
- 2xx SuccessRequest succeeded
- 3xx RedirectionAnother destination
- 4xx Request failureInterpret this request404 belongs here
- 5xx Server failureServer could not fulfil
- 6xx Global failureFailure across destinations
Read the status with its request method and call leg. For example, 200 after REGISTER confirms a binding; it does not prove an INVITE succeeded.
What this response means
The recipient does not find the addressed user or resource in the domain it is handling. It is a SIP routing result, not an HTTP web-page error.
Read it in context
Wrong destination domains, number normalization or missing dialplan destinations can be involved. A carrier can also map downstream routing problems into this response, so the rejecting leg matters.
Administrator checks
Compare the dialed digits with the final request URI after handset and PBX transformations. Confirm the expected context, destination and trunk. For incoming calls, inspect the delivered DID and its match rather than assuming the invoice format is used.
Next action and common mistake
Do not create a catch-all paid route merely to suppress 404. Repair the intended mapping and test nearby legitimate and invalid destinations. Keep a missing local extension separate from an upstream carrier’s inability to route the number.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.