# REST API — Error codes


Source: https://vertexsms.com/en/api/errors

These error codes appear in callbacks from VertexSMS to your endpoints (delivery reports, HLR results). Errors on outgoing API calls (requests you make to VertexSMS) are reported via standard HTTP status codes — see the Introduction.

| Code | Description |
|------|-------------|
| 0 | No error. |
| 1 | Error from MSC: illegal subscriber. |
| 2 | Message not delivered — validity period expired. |
| 20 | Country or operator not configured for your account. |
| 21 | SMS blocked by filter (e.g. number blacklisted). For details contact `support@vertexsms.com`. |
| 22 | Duplicate SMS. |
| 23 | Limit of max SMS to one number reached. |
| 24 | Account balance limit reached. |
| 40 | HLR error: subscriber unknown (probably not in operator database). It is normal to retry after some time; if it persists, the MSISDN is likely retired. |
| 41 | HLR error: SMS service barred for the subscriber (operator blocking P2P SMS). |
| 43 | HLR error: subscriber absent (out of network range or phone off). |
| 51 | Other / unknown HLR error — contact VertexSMS support. |
| 53 | Invalid MSISDN. |
| 999 | Unknown VertexSMS API error. |