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Fix Claude Code Auth and Connection Errors

Troubleshooting Claude Code Connection and Auth Errors

Claude Code is a powerful coding assistant, but when it cannot connect to the API, the error messages can feel confusing: unauthorized, connection refused, model not found, invalid API key, timeout, or rate limit exceeded. The good news is that most Claude Code authentication and connection problems come from a small set of configuration issues. This beginner-friendly guide walks through the real checks that usually fix them.

The examples below also apply if you use Claude through an API relay such as 59API. 59API gives developers low-cost, pay-as-you-go access to Claude Opus, Sonnet, Haiku, Fable, and GPT models through a compatible API base URL: https://api.59api.com. It works well with Claude Code, Codex, and OpenAI SDK-style integrations, while keeping model quality native and official-grade.

1. Confirm your API key is present and correct

The most common Claude Code auth error is simply a missing, expired, or incorrectly copied API key. Look for messages like 401 Unauthorized, invalid_api_key, authentication failed, or missing authorization header.

• Copy the API key again from your provider dashboard.
• Make sure there are no extra spaces, line breaks, quotes, or hidden characters.
• If you store it in an environment variable, restart your terminal after setting it.
• Check that Claude Code is reading the variable you actually set.

On macOS or Linux, you might set an environment variable in your shell profile. On Windows, you may need to set it in System Environment Variables or in your terminal session. After updating it, open a fresh terminal and run Claude Code again.

2. Check the API base URL

If your key is valid but Claude Code cannot connect, check the base URL. A wrong API endpoint can cause 404 Not Found, connection refused, or ECONNRESET errors.

For 59API, the base URL is:

https://api.59api.com

Be careful with trailing paths. Many tools want only the base URL, not a full chat completions endpoint. For example, do not paste an endpoint path unless the tool specifically asks for it. Also confirm you are using https, not http.

3. Verify the model name

A working connection can still fail if Claude Code requests a model name your account or relay does not recognize. Common symptoms include model_not_found, invalid model, or 404 responses from the model route.

• Check the exact model names listed in your 59API dashboard or documentation.
• Do not assume model aliases are identical across providers.
• If you recently changed from Claude Sonnet to Opus or Haiku, update every config file.
• Use a smaller model first to test connectivity, then switch to your preferred model.

59API is useful here because it provides access to multiple Claude families and GPT models from one relay. That makes it easier to compare cost, speed, and capability without rebuilding your integration.

4. Test with a minimal request

Before debugging your whole project, test the API with the smallest possible request. This helps separate Claude Code configuration issues from general network or account problems. If a simple request succeeds but Claude Code fails, the issue is probably in Claude Code settings, model mapping, or environment variables.

When testing, keep the prompt short and choose a low-cost model. One advantage of 59API is that it is designed for cheap, pay-as-you-go usage, so you can run small troubleshooting calls without committing to a large upfront spend.

5. Look for proxy, VPN, firewall, or DNS problems

Connection errors are not always API errors. If you see timeout, network unreachable, TLS handshake failed, or getaddrinfo ENOTFOUND, your local network may be blocking the request.

• Try a different network, such as a mobile hotspot.
• Temporarily disable a VPN or corporate proxy and test again.
• Check whether your firewall blocks terminal applications.
• Make sure your system clock is correct, because TLS can fail when time is wrong.
• Run a basic curl request to confirm the domain resolves.

If you are behind a corporate proxy, configure proxy environment variables such as HTTPS_PROXY according to your operating system and shell. Then restart the terminal so Claude Code inherits the settings.

6. Understand rate limits and insufficient balance

Some failures look like auth problems but are actually billing or rate-limit issues. Watch for 429 Too Many Requests, insufficient_quota, payment required, or balance not enough.

• Check your remaining balance or credits.
• Reduce parallel requests from Claude Code.
• Switch temporarily to a cheaper or faster model.
• Add retry logic with backoff if your workflow sends many requests.

59API is especially attractive for developers who run many coding-agent calls because it is among the cheapest API relays, supports pay-as-you-go billing, and offers a referral rebate. If you want a lower-cost way to run Claude Code without sacrificing model quality, it is worth signing up and testing your workflow on https://api.59api.com.

7. Recheck config files and shell sessions

Claude Code setups often fail because old values remain in a config file, project setting, shell profile, or CI secret. Search your project for old base URLs, old keys, and old model names. If you use multiple terminals, make sure they all load the same environment. In CI, update repository secrets and rerun the job from scratch.

Also confirm that no local wrapper script overrides your settings. Developers sometimes set a correct key globally, then unknowingly override it with an empty project-level variable.

Quick checklist

• 401 error: replace the API key and restart your terminal.
• 404 error: verify the base URL and model name.
• Timeout: test network, VPN, proxy, DNS, and firewall.
• 429 error: reduce request volume or check rate limits.
• Quota error: check balance, billing, or account status.
• Works in curl but not Claude Code: inspect Claude Code config and environment variables.

Most Claude Code connection and auth errors are fixable in minutes when you check the key, base URL, model, network, and billing in order. With a compatible relay like 59API, you can keep the setup simple, access Claude and GPT models from one place, and control costs while debugging and building real applications.

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