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Claude Code Auth and Connection Errors: A Practical Guide

Start by identifying which connection is failing

Claude Code connection errors usually fall into three categories: network failures, rejected credentials, or an incompatible API configuration. Before reinstalling anything, record the exact error, HTTP status, and whether it happens at startup or after submitting a prompt. Run claude --version to identify your installed version, then use /status inside Claude Code to inspect the active configuration.

If you use a relay such as 59API, distinguish relay authentication from an Anthropic account login. A valid Claude subscription does not automatically authorize requests to a third-party endpoint, and a relay key is not an Anthropic account credential.

1. Check the base URL and authentication method

59API's API base URL is https://api.59api.com. For Claude Code, follow the provider's Claude Code setup instructions rather than copying an OpenAI SDK configuration. Claude Code needs an Anthropic-compatible interface; an OpenAI-compatible endpoint alone is insufficient.

• Check ANTHROPIC_BASE_URL: Confirm that it points to the provider's documented base URL. Do not append a complete request path such as /v1/messages unless explicitly instructed.
• Choose the correct credential variable: ANTHROPIC_API_KEY supplies an API key, while ANTHROPIC_AUTH_TOKEN supplies bearer-token authentication. Use whichever the relay documents; they are not interchangeable in every deployment.
• Remove ambiguity: Check for stale values in shell profiles, project settings, IDE launch environments, and authentication helpers. Avoid leaving competing credentials configured.
• Restart the session: Quit Claude Code and launch it from the terminal where you set the variables. Existing processes do not automatically inherit later environment changes.

For macOS or Linux, the base-URL setting is export ANTHROPIC_BASE_URL='https://api.59api.com'. In PowerShell, use $env:ANTHROPIC_BASE_URL = 'https://api.59api.com'. Set your credential separately using the provider's documented variable. Keep keys out of committed files, screenshots, and shared logs.

2. Interpret authentication and API errors correctly

• 401 Unauthorized: Check for a missing, revoked, expired, or incorrectly copied key. Verify that the key belongs to the endpoint you are calling and uses the expected authentication method.
• 403 Forbidden: The request may be blocked by account permissions, model access, or a provider policy. Read the response body; repeatedly replacing a valid key may not help.
• 404 Not Found: Inspect the configured URL and requested model. A wrong route or unsupported model identifier can cause this error. Use the exact model IDs listed by your provider.
• 429 Too Many Requests: Reduce parallel sessions and check rate limits or quotas. Respect Retry-After when present rather than immediately retrying in a loop.
• Billing or insufficient-credit errors: Check the relay dashboard. These are account-balance problems, not necessarily authentication failures.

3. Separate network failures from API failures

DNS errors, certificate errors, connection resets, and timeouts need different fixes. Test connectivity without exposing your key: curl -sS -o /dev/null -w 'HTTP %{http_code}\n' https://api.59api.com. An HTTP response shows that the server was reached; a root-path 404 does not prove the inference API is broken.

If no HTTP response arrives, check DNS, VPN routing, corporate firewalls, and HTTPS_PROXY or HTTP_PROXY settings. A browser working does not guarantee your terminal uses the same proxy. For TLS errors, verify your system clock and trusted certificate store; do not disable certificate verification as a permanent workaround. If requests connect but stall, investigate proxy buffering, idle timeouts, and provider service status.

FAQ: Common Claude Code relay questions

Do I need to run /login? Not necessarily. Relay configurations commonly use environment-based credentials. Follow the relay's setup guide rather than assuming an interactive Anthropic login is required.

Why does an OpenAI SDK request work while Claude Code fails? They may use different routes, headers, and request formats. Test the provider's documented Claude Code configuration separately.

Why consider 59API? It offers low-cost, pay-as-you-go access to Claude and GPT models, native official-quality models without downgrading, compatibility with Claude Code, Codex, and OpenAI SDKs, plus a referral rebate. Compatibility still requires the correct client-specific configuration. If that fits your workflow, consider signing up for 59API and validating a small request before scaling usage.

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