# Failed API Requests Are you running into any issues with MessageBird's REST API? Here is a list of the most common API issues. Error codes When using our REST API, please keep in mind that there are different error codes for different purposes: * HTTP status codes If you forgot to enter the recipient, you might encounter error 204 which will indicate that there is data missing. When using an incorrect Access Key or Username/Password combination you will face error 401, this indicates that the authorization data is incorrect. MessageBird uses standard HTTP status codes to indicate the success or failure of an API request. You can check all the details on HTTP status codes in our documentation [here](https://developers.messagebird.com/api#api-errors). * Error Codes If we take the examples from the HTTP status codes above, you would receive error code 11 for missing data. Incorrect authorization data will return error 15. Error codes provide error information for failed Voice API calls. You can check all the details for the errors [here](https://developers.messagebird.com/docs/voice-calling/troubleshooting/#voice-error-codes). If you have any remaining questions about the error codes, please do not hesitate to [submit a request](https://support.messagebird.com/hc/en-us/requests/new) to our Support team for further assistance. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.bird.com/connectivity-platform/troubleshooting-voice/failed-api-requests.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.