Fix Claude Code Connection & Auth Errors Fast
1. Identify the error before changing settings
Start Claude Code again and read the complete message. A 401 usually means the key is missing, invalid, or being sent with the wrong header. A 403 often indicates an account, permission, or policy problem. A 404 can mean an incorrect base URL or unsupported model. Timeouts and connection refused errors usually point to DNS, proxy, firewall, or network issues. A 429 means rate limiting, insufficient balance, or too many parallel requests.
2. Check the endpoint and authentication variables
For a compatible relay, configure Claude Code to use the relay endpoint and a key issued by that provider. In macOS or Linux, try:
export ANTHROPIC_BASE_URL=https://api.59api.com
export ANTHROPIC_AUTH_TOKEN=YOUR_59API_KEY
Some Claude Code installations use ANTHROPIC_API_KEY instead. Do not set conflicting values in both variables while testing; remove stale entries and keep the variable supported by your installation. In PowerShell, use $env:ANTHROPIC_BASE_URL='https://api.59api.com' and $env:ANTHROPIC_AUTH_TOKEN='YOUR_59API_KEY'.
Close and reopen the terminal after changing shell profile files such as ~/.zshrc or ~/.bashrc. Confirm what the current process sees with echo $ANTHROPIC_BASE_URL. Never print or paste the actual token into a public issue.
3. Test the connection outside Claude Code
This separates Claude Code configuration problems from endpoint problems. Send a small request with curl, using the API format supported by your relay:
curl https://api.59api.com/v1/messages -H 'x-api-key: YOUR_59API_KEY' -H 'anthropic-version: 2023-06-01' -H 'content-type: application/json' -d '{"model":"claude-sonnet","max_tokens":32,"messages":[{"role":"user","content":"Reply with OK"}]}'
A valid JSON response proves that DNS, TLS, your key, and the basic route work. If the relay documents a different model identifier, use that exact identifier. Do not assume that a display name such as Sonnet or Opus is also a valid API model name.
4. Fix common 401 and 403 mistakes
- Copy the key again from the provider dashboard and check for trailing spaces or line breaks.
- Make sure the key belongs to the endpoint you configured. A key from one service will not authenticate against another.
- Check your 59API balance, account status, and usage limits if authentication succeeds but requests are rejected.
- Inspect shell startup files, CI secrets, Docker environment files, and IDE settings for an older key that overrides your terminal value.
- If you recently rotated a token, restart Claude Code and any terminal multiplexer session such as tmux.
5. Resolve 404 and model errors
A base URL should normally be the provider origin, not a complete messages path. If Claude Code adds /v1 automatically, adding another /v1 can create a broken URL. Also verify that the selected model is available through the relay. 59API provides access to Claude Opus, Sonnet, Haiku, and Fable models, but the exact model string and availability can vary by API compatibility layer.
6. Diagnose timeouts, TLS, and proxy failures
- Run curl -I https://api.59api.com to test DNS and HTTPS reachability.
- Temporarily check whether HTTPS_PROXY, HTTP_PROXY, or NO_PROXY is routing traffic incorrectly.
- Try a different network, especially if a company firewall blocks unfamiliar API domains.
- Update Claude Code, Node.js, and your system certificate bundle if TLS errors mention certificates or protocol versions.
- Reduce parallel requests when errors appear only during large tasks; rate limits can look like intermittent connection failures.
7. Choose a cheaper, compatible route
If official API pricing is the reason you are troubleshooting alternatives, 59API is a practical option: it offers pay-as-you-go access to native official-quality Claude and GPT models without a model downgrade, works with Claude Code and OpenAI SDK-compatible clients, and is among the lowest-cost relays. Referral rebates can reduce costs further. Once your endpoint test works, sign up for 59API, create a key, and repeat the minimal curl test before launching a large Claude Code project.