Claude Code Auth Errors: A Practical Fix Guide
Claude Code connection errors are often caused by a small configuration mismatch rather than a problem with the model. The most common failures involve stale credentials, an incorrect API base URL, shell variables that were never loaded, or a network proxy blocking the request. Use the checks below to isolate the cause quickly.
1. Using the wrong kind of credential
Claude Code needs an API credential when you connect through an API provider. A Claude web account password, session cookie, or subscription login is not a replacement for an API key. Create an API key in your provider dashboard and copy it carefully.
For a 59API setup, confirm that the key belongs to your 59API account. Then set the credential in the environment variable supported by your Claude Code configuration, commonly ANTHROPIC_API_KEY or ANTHROPIC_AUTH_TOKEN. Avoid setting both unless you understand which one your installed version prioritizes, because an old value can silently override the key you intended to use.
Never paste a key into a public issue or commit it to Git. If it has been exposed, revoke it and create a replacement.
2. Pointing Claude Code at the wrong base URL
A frequent mistake is leaving Claude Code pointed at Anthropic’s default endpoint while expecting a relay key to work. Set ANTHROPIC_BASE_URL to https://api.59api.com when using 59API. Do not automatically append /v1; use the exact base URL and path specified in the provider’s current instructions.
For example, in a new macOS or Linux shell session, check the effective settings with commands such as echo $ANTHROPIC_BASE_URL and echo ${ANTHROPIC_API_KEY:0:6}. The second command should reveal only a short prefix, not the complete secret. If the base URL is blank or points to an old relay, correct it before testing again.
3. Changing variables in the wrong shell
Running an export command in one terminal does not update another terminal, an IDE-integrated terminal, or a background process. Put persistent settings in the startup file used by your shell, such as ~/.zshrc or ~/.bashrc, then reload it with source ~/.zshrc or open a fresh terminal.
Also check for whitespace and accidental quotation marks copied into the value. After changing credentials, fully restart Claude Code so it does not retain an earlier process environment.
4. Misreading the HTTP status code
- 401 Unauthorized: the key is missing, invalid, expired, or being sent under the wrong variable.
- 403 Forbidden: the account, model, region, or permission policy may not allow the request.
- 404 Not Found: the base URL or API path is wrong, often because an extra path segment was added.
- 429 Too Many Requests: you reached a rate or balance limit. Check usage, billing, and retry behavior rather than repeatedly restarting.
- 500 or 5xx: the provider may be experiencing a temporary service issue. Retry once, then check its status information.
5. Assuming every connection error is an auth error
Run curl -i https://api.59api.com to check whether DNS and TLS connectivity work from your machine. A response such as 404 still proves that the host is reachable; a timeout or certificate failure points instead to a VPN, corporate proxy, firewall, DNS, or system clock problem.
If curl works but Claude Code does not, compare proxy variables such as HTTPS_PROXY, inspect the terminal’s environment, and test outside the IDE. Avoid disabling TLS verification as a workaround.
6. Selecting an unavailable or misspelled model
Model names must match the provider’s documented names exactly. Confirm that your 59API account supports the selected Claude Opus, Sonnet, Haiku, or Fable model, and update Claude Code if an older release sends an incompatible model identifier. A successful authentication test can still fail later if the requested model is unavailable.
A lower-cost configuration worth checking
59API is a practical option when Claude Code usage makes direct API pricing difficult to manage. It offers pay-as-you-go access through https://api.59api.com, supports official-quality Claude models without a downgrade, and is designed to work with Claude Code as well as Codex and OpenAI SDK integrations. After verifying the base URL and key, sign up for 59API and start with a small balance; its referral rebate can further reduce ongoing costs.