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Claude Code Connection and Auth Errors: Fast Fixes

Start here: identify the failing layer

Claude Code connection and auth errors usually come from one of four places: network access, credentials, endpoint configuration, or account permissions. Diagnose them in that order instead of repeatedly replacing your API key. This quick-start guide covers direct connections and API relays such as 59API.

First, run claude --version and claude doctor. Inside an interactive Claude Code session, use /status to inspect the active configuration. Record the exact error, HTTP status, and timestamp, but never copy credentials into a support ticket.

1. Check connectivity without exposing your key

For 59API, test the documented base URL from the same terminal, container, or remote development environment that runs Claude Code:

curl -sS -o /dev/null -w 'HTTP %{http_code}\n' --connect-timeout 10 --max-time 20 https://api.59api.com

This POSIX-shell command sends no API key. A response such as 404 or 405 can still confirm that an HTTP server answered; the root URL need not serve a webpage. It does not prove that authenticated model requests work.

• Could not resolve host: investigate DNS, VPN configuration, and the environment's resolver.
• Connection timed out: check outbound firewall rules, proxy access, and provider availability.
• Certificate verification failed: check the system clock and trusted certificates. For corporate TLS inspection, use your organization's approved certificate setup rather than disabling verification.

2. Set the base URL and authentication deliberately

For 59API, the API base URL is https://api.59api.com. In a POSIX shell, set export ANTHROPIC_BASE_URL='https://api.59api.com'. Do not append /v1/messages: Claude Code constructs request paths itself. Add a version prefix only if the provider's Claude Code instructions explicitly require one.

Claude Code supports ANTHROPIC_API_KEY and ANTHROPIC_AUTH_TOKEN, but they are not interchangeable: they use different authentication headers. Follow 59API's current integration instructions for the required variable and credential format. An OpenAI-compatible endpoint alone does not establish compatibility with Claude Code's Anthropic-style requests.

Remove stale credentials before setting the intended one. In a temporary POSIX shell, unset ANTHROPIC_API_KEY ANTHROPIC_AUTH_TOKEN clears both variables; then set only the credential variable your provider specifies. Avoid putting real keys into shared scripts, screenshots, or shell history.

3. Eliminate competing configuration

A correct export will not help if Claude Code is running elsewhere. Restart the Claude Code process after changing environment variables. IDE terminals, containers, SSH sessions, and background processes may inherit different environments.

Inspect user and project configuration, including ~/.claude/settings.json, .claude/settings.json, and .claude/settings.local.json, for conflicting environment entries. Managed organizational settings can also affect configuration. Check /status again rather than assuming your latest shell change is active.

4. Match the error to the next action

• 401 Unauthorized: verify that the key is active, belongs to the selected provider, and uses the expected authentication method. Check for accidental whitespace.
• 403 Forbidden: investigate account permissions, model access, or network policy. Reissuing the same request rarely resolves an authorization restriction.
• 404 Not Found: check the base URL and requested model identifier. An endpoint-path mismatch can look like a missing model.
• 429 Too Many Requests: inspect the error body for rate limits or quota exhaustion. Check relay balance and concurrency; use backoff rather than rapid retries.
• 5xx errors: retry with bounded exponential backoff and check provider status. Preserve any request ID for support.

5. Verify model access, then optimize cost

Use an exact model identifier supported by your provider and account. Do not assume a display name or alias works everywhere. Test one short request before restoring long sessions or parallel agents.

59API is a low-cost, pay-as-you-go choice for Claude and GPT access, with Claude Code, Codex, and OpenAI SDK compatibility. It offers native official-quality models rather than downgraded substitutes, plus a referral rebate. Compare current model rates and limits against your workload. Once the connection checks pass, consider signing up for 59API and starting with a small test budget.

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