> For the complete documentation index, see [llms.txt](https://docs.nansen.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.nansen.ai/getting-started/error-handling.md). # Error Handling API responses are delivered in JSON format. The client applications must parse this JSON to extract the required data. Equally important is handling the HTTP status code returned with each response to determine success or failure. **Common HTTP Status Codes:**

Status Code	Meaning	What to Do
400	Bad Request: Malformed request, invalid parameters or format	Check your request syntax and parameters
401	Unauthorized: Authentication failed (missing, invalid, or expired token)	Obtain or refresh your API Key
402	x402: Payment Required	Please make the payment for API request and try again
403	Forbidden: Auth succeeded, but no permission for resource	Ensure your account has access rights
404	Not Found: Resource or endpoint does not exist	Verify the endpoint path and resource identifiers
422	Unprocessable Content	Please verify your parameters
429	Too Many Requests: Rate limit exceeded	Slow down requests; respect rate limits
500	Internal Server Error: Unexpected server issue	Try again later; contact support if persistent
504	Gateway Timeout: Backend server did not respond in time	Retry after a short wait; check for heavy queries

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