# What do telephony & error codes mean?

#### These are the most common error codes

| **401 Invalid credentials** | The SIP ID or SIP password is incorrect.                                                                                 |
| --------------------------- | ------------------------------------------------------------------------------------------------------------------------ |
| **404 Number unknown**      | The number doesn't exist, isn't assigned to a connection, or isn't configured in the recipient's device or phone system. |
| **486 Busy**                | The recipient's line is currently busy.                                                                                  |
| **487 Call ended**          | Standard signal when the other party hangs up.                                                                           |

#### Other commonly transmitted codes

| **100 Trying**                        | Call setup in progress.                                |
| ------------------------------------- | ------------------------------------------------------ |
| **180 Ringing**                       | The recipient's device is signaling an incoming call.  |
| **183 Session progress**              | Connection is being established.                       |
| **200 OK**                            | Call accepted or device registered.                    |
| **301 Moved permanently**             | Permanent call forwarding active.                      |
| **302 Moved temporarily**             | Temporary call forwarding active.                      |
| **400 Bad request**                   | Incorrect parameters in the request.                   |
| **403 Forbidden**                     | No permission to place this call.                      |
| **407 Proxy authentication required** | Authentication needed for outbound calls.              |
| **408 Request timeout**               | No response, possibly due to network issues.           |
| **480 Temporarily unavailable**       | Recipient unavailable (e.g., DND active).              |
| **481 Call does not exist**           | Status message not received.                           |
| **482 Loop detected**                 | Call forwarding loop detected.                         |
| **488 Not acceptable here**           | Unsupported codec, encryption, or transmission method. |
| **500 Server error**                  | General server issue.                                  |
| **502 Bad gateway**                   | Incorrect or faulty gateway.                           |
| **503 Service unavailable**           | SIP service temporarily down.                          |
| **603 Declined**                      | Call rejected manually or automatically.               |