Session Initiation Protocol (SIP) response codes and timing patterns are used in detecting invalid and no-answer numbers. The following table describes the common SIP response codes.
| SIP Response Code | Description |
|---|---|
| 200, "OK" | Indicates that the request was successful. |
| 403, "Forbidden auth ID" | Indicates that the server has refused to fulfill the request. Authorization does not fix the issue. |
| 403, "No Active Session" | Indicates that an active session does not exist. |
| 403, "No Headers" | Indicates that the WebRTC call does not contain header information. |
| 403, "No password in memory" | Indicates invalid credentials for LiveVox Communicator or LiveVox Telephone. |
| 403, "Preload Route denied" | Indicates that the destination or route is not supported. |
| 404, "No destination" | Indicates that the server has definitive information that the user does not exist at the domain specified in the request URI. Also, this status is returned if the domain in the request URI does not match any of the domains handled by the recipient of the request. |
| 404, "Not here" | Indicates that the destination you are trying to reach is not reachable. |
| 480, "No routing pool available" | Indicates an internal routing message. |
| 483, "Too Many Hops" | Indicates that the server is rejecting bad calls. |
| 500, "Internal Error" | Indicates that the server could not fulfill the request due to an unexpected condition. |
| 503, "Service Unavailable" | Indicates that the server is temporarily unable to process the request due to a temporary overloading or maintenance of the server. The server might indicate when you should retry the request in a Retry-After header field. |