WHMCS API uses standard HTTP status codes in the response header:
| Code | Description |
|---|---|
| 200 | Success |
| 202 | You must provide a second authentication factor to finish login. |
| 401 | Unauthorized Usually, this indicates that the username or password is not valid or the system denied the requested access. |
| 403 | Forbidden Usually, this indicates that the IP address is banned due to too many login failures or it is not whitelisted (when WHMCS API IP restriction is enabled). |
| 404 | Not Found |
| 412 | Precondition Fail Usually, this indicates that Two-Factor Authentication is required or the provided Two-Factor Authentication token is invalid. |
| 422 | Invalid input |
| 500 | Internal Server Error |