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Claude API Error Codes & Troubleshooting Guide

Fix common Claude API errors fast. Covers error codes 400, 401, 402, 429, 500, and 529 with causes, solutions, and debugging tips.

Common Claude API Error Codes

When working with the Claude API, you will encounter HTTP error codes that indicate what went wrong. This guide covers the most common ones, explains their causes, and shows you how to fix them.

400 — Bad Request

What it means: Your request body is malformed or contains invalid parameters.

Common causes:

  • Missing required fields like model or messages
  • Invalid max_tokens value (must be a positive integer)
  • Malformed JSON in the request body
  • Sending an empty messages array
  • Using a role other than user or assistant in messages

    • Fix: Validate your request payload against the API schema. Check that all required fields are present and correctly typed. Use a JSON linter if you suspect formatting issues.

    401 — Unauthorized

    What it means: Your API key is missing, invalid, or expired.

    Common causes:

  • Missing x-api-key header or Authorization header
  • Typo in the API key string
  • Using a revoked or deleted key
  • Mixing up keys between environments

    • Fix: Double-check your API key in the dashboard. Make sure you are passing it in the correct header. Regenerate the key if needed.

    402 — Insufficient Balance

    What it means: Your account does not have enough credits to process the request.

    Common causes:

  • Balance has been fully consumed
  • The estimated cost of the request exceeds your remaining balance

    • Fix: Top up your balance through the dashboard. On claudeapi.cheap, you can add funds instantly with crypto (USDT, BTC, ETH).

    429 — Rate Limited

    What it means: You are sending too many requests in a short time.

    Common causes:

  • Exceeding your plan's requests-per-minute limit
  • Sending burst traffic without any throttling
  • Multiple services sharing the same API key

    • Fix: Implement exponential backoff in your retry logic. Space out requests or upgrade your plan for higher rate limits. On claudeapi.cheap, Pro and Ultimate plans offer up to 500 req/min.

    500 — Internal Server Error

    What it means: Something went wrong on the server side.

    Common causes:

  • Temporary server issues
  • Upstream model errors
  • Unexpected input that triggers a server-side bug

    • Fix: Retry the request after a short delay. If the error persists, check the API status page. Do not retry immediately in a tight loop — use exponential backoff starting at 1-2 seconds.

    529 — Overloaded

    What it means: The API is experiencing unusually high traffic and cannot process your request.

    Common causes:

  • High demand across all users
  • Capacity limits during peak hours

    • Fix: Wait and retry with exponential backoff. This is a temporary condition. Avoid aggressive retry loops, which can make the problem worse.

    Debugging Tips

  • Log full responses — Always log the complete error response body, not just the status code. The error.message field often contains specific details about what went wrong.
  • Use try/catch blocks — Wrap every API call in error handling. Never let an unhandled API error crash your application.
  • Implement retries with backoff — For 429, 500, and 529 errors, use exponential backoff. A good pattern is to wait 1s, 2s, 4s, 8s between retries with a maximum of 3-5 attempts.
  • Validate before sending — Check your request payload locally before making the API call. Catch 400 errors before they happen.
  • Monitor your usage — Track your request volume and balance to avoid unexpected 402 or 429 errors in production.

    • Need Help?

    If you are using claudeapi.cheap and encounter persistent errors, reach out through our Telegram support channel. We monitor API health around the clock and can help troubleshoot issues specific to your integration.

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