Claude Troubleshooting Guide: Complete List of Common Error Codes & Proven Fixes

Running into errors while using Claude can be frustrating. Whether you're an API developer or a regular user, every common error code has a reliable fix. This guide breaks down the most frequent Claude errors and walks you through tested solutions to get your chats or API calls back on track fast.

API Request Errors: Rate Limits & Authentication Failures

The most common error when calling the Claude API is a rate limit error (HTTP 429 Too Many Requests). This happens when you exceed your account tier's allowed requests per unit time — you'll need to adjust your call frequency or upgrade your plan. The fix is to implement exponential backoff retry logic in your code and double-check that your API Key is correctly set as an environment variable.

Another frequent issue is authentication failure (HTTP 401 Unauthorized), usually caused by an expired API Key, extra spaces when copying the key, or a revoked key. Head to the Anthropic console to generate a new key, and confirm that the x-api-key header in your request is formatted correctly. If you're using a reverse proxy, also verify that the proxy isn't altering your authentication credentials.

Conversation Interruptions & Context Loss Errors

In long conversations, Claude may show a "Conversation too long" or "Token limit exceeded" warning. This means the combined input and output have exceeded the model's context window (e.g., Claude 3.5 Sonnet supports 200K tokens). Manually trim your message history, keeping only essential parts, or use the max_tokens parameter to control output length and avoid generating overly long content in a single turn.

Some users encounter a "Chat prematurely terminated" error, often due to network instability or server-side timeouts. Check your local network connection, switch to a wired connection, or try a different proxy node. If it happens frequently, adjust your client timeout settings to 60 seconds or more.

Account Lockouts & Subscription Errors

Claude Pro users sometimes see "Payment declined" or "Billing error" when renewing. Common causes include insufficient card balance, issuer fraud blocks, or mismatched billing addresses. Try using an international payment card that supports global transactions, and make sure the billing info matches what your bank has on file. If you're using a virtual card, verify that 3D Secure is enabled.

Another error, "Account locked", is often triggered by security protections when logging in from an unusual location. Sign in to your Anthropic account, go to security settings to unlock the device, or recover access via email verification. Avoid switching IPs or regions too frequently to reduce the risk of false positives.

Model Unavailable & Parameter Errors

If you get a "Model not found" error when calling the API, the model name you requested is either misspelled or deprecated. Always check the official docs for the current model identifier — for example, Claude 3.5 Sonnet's official name is claude-3-5-sonnet-20241022. Also review your request parameters to make sure you aren't including unsupported fields, such as the old stream parameter, which has been replaced by stream_options in newer models.

When you see "Invalid request body", it's usually a JSON formatting issue or a missing required field. Use a JSON validator to check your payload, ensuring the messages array is structured correctly and every message includes both role and content properties. We recommend using the official SDK rather than manually constructing requests, as it automatically avoids most formatting pitfalls.