Encountering errors or connection issues while using Claude? This guide covers common Claude error codes and account lag problems, offering real, actionable troubleshooting steps to help you restore smooth conversations and avoid wasting credits through repeated trial and error.
API Returns 401 Unauthorized Error
When you call the Claude API and receive a 401 error, it usually means the API key is invalid or expired. First, log in to the Anthropic console to check the key status and confirm whether it is inactive or has insufficient balance. If the key was just generated, wait about 5 minutes before retrying—system sync can sometimes be delayed.
Another common cause is accidentally copying extra spaces or line breaks with the key. We recommend typing the key manually rather than copy-pasting, paying close attention to hidden whitespace characters at the beginning or end. If the issue persists, generate a new key to replace the old one—once deleted, the old key becomes immediately invalid.
Handling Request Timeouts & Connection Drops
If Claude requests hang for a long time or disconnect mid-stream, it is often due to unstable network conditions or proxy server configuration issues. Start by testing your local network speed; if latency exceeds 300ms, switch to a more stable Wi-Fi connection or use wired Ethernet. If you are using a proxy, ensure the node supports the WebSocket protocol—some free nodes block long-lived connections.
Additionally, the official Claude API has concurrency limits; frequent rapid-fire requests can easily trigger throttling. Increase the interval between requests to at least 2 seconds, or check your code for loops causing repeated calls. If you experience lag on the web version, try clearing your browser cache and logging back in.
Account Locked or "Suspicious Activity" Warning
If your account suddenly cannot log in and displays a "suspicious activity" warning, it is often caused by abnormal cross-IP access frequency within a short period. For example, logging in at home and then using your mobile hotspot in another city can trigger the system to flag the account as risky. Solution: verify your identity via email on your usual device, then unlock the account. After that, avoid switching between more than 3 different IPs within 14 days.
If you use multiple accounts, we recommend binding each account to a separate email and device identifier. Claude’s detection mechanism monitors login device fingerprints; frequently switching between accounts on the same device can lead to all accounts being flagged. Consider assigning each account its own browser profile or using incognito windows in different sessions.
Messages Sent but No Response or Repeated Replies
Sometimes Claude keeps spinning after you send a message, or it replies with the same content as the previous turn. This is often due to the conversation context exceeding the model limit, or the history containing error symbols that cause parsing issues. You can manually clear the current session and start a new conversation. If the problem persists, check whether your input includes unusual Unicode characters—such as special tab characters or invisible control characters—and delete them before retrying.
Additionally, the free version of Claude has a per-hour message cap. When the limit is reached, the interface may not show an immediate warning, but subsequent requests will be blocked. Check your account usage panel to confirm whether you have hit your quota. If none of these apply, it could be a temporary server issue on Anthropic’s end—wait 15 minutes and refresh the page to try again.
