Claude Troubleshooting & Diagnostic Guide

1. Login Failure Diagnosis (403/429/500)

Login failures typically map to specific root causes based on HTTP status codes and error messages:

Error Code Matrix

Diagnostic Procedure

# 1. Check current IP reputation
curl https://ipinfo.io
# Verify "org" does not show datacenter ASN (AWS, Hetzner, etc.)

# 2. Test DNS resolution
nslookup claude.ai
# Should resolve to Cloudflare IPs (104.18.x.x range)

# 3. Clear browser state completely
# Chrome: Settings → Privacy → Clear browsing data → All time → Cookies, Cache
# Firefox: Settings → Privacy → Clear Data → Everything

# 4. Test login with clean profile
google-chrome --user-data-dir="/tmp/test-profile" --proxy-server="socks5://proxy:1080"

2. API Call Exception Troubleshooting

API failures require systematic diagnosis of network, authentication, and rate limiting issues:

Common API Errors

• 401 Unauthorized: Invalid API key or key revoked. Verify key in Anthropic Console, regenerate if needed.
• 429 Rate Limit: Organization exceeded RPM (requests per minute) or TPM (tokens per minute) quota. Implement client-side rate limiting.
• 529 Overloaded: Anthropic backend at capacity. Retry with exponential backoff (2^n seconds with jitter).
• Timeout: Request exceeded 60-second timeout. Split large prompts into smaller chunks or reduce max_tokens.

API Debug Script

#!/usr/bin/env node
const Anthropic = require('@anthropic-ai/sdk');

async function diagnoseAPI() {
  const client = new Anthropic({
    apiKey: process.env.ANTHROPIC_API_KEY,
  });

  try {
    console.log('Testing API connectivity...');
    const response = await client.messages.create({
      model: 'claude-sonnet-4.5-high',
      max_tokens: 100,
      messages: [{ role: 'user', content: 'Hello' }],
    });
    console.log('✓ API key valid, connection successful');
    console.log('Response:', response.content[0].text);
  } catch (error) {
    console.error('✗ API Error:', error.status, error.message);
    if (error.status === 401) console.log('→ Check API key validity');
    if (error.status === 429) console.log('→ Rate limit exceeded, wait 60s');
    if (error.status === 529) console.log('→ Backend overloaded, retry with backoff');
  }
}

diagnoseAPI();

3. Payment Binding Failure Root Cause

Anthropic does not receive the bank's reason for a decline, so work through the likely causes in order. The payment methods guide has the full official checklist:

• Card Declined: Insufficient balance, an invalid CVV, or an expired card. Make sure the balance covers the full amount.
• Card Type Not Accepted: Pro and Max list credit and debit cards only, so a prepaid card can be declined for that reason alone. Anthropic does not publish blocked BINs.
• Address Mismatch: The billing address must match your bank's record and the card's country of origin, and be an eligible billing location.
• 3D Secure Not Completed: Confirm the SMS code or bank app prompt when your bank asks for it.
• Repeated Attempts: Retry once, then ask your bank. Only the card issuer can explain a decline.

4. Common Issues FAQ & Quick Fixes

Q: "Claude says my session expired, but I just logged in"

A: Session cookies are tied to IP and device fingerprints. Rapid IP changes invalidate sessions. Solution: Enable 2FA to reduce re-verification prompts, maintain consistent IP per session.

Q: "API returns cached responses to new prompts"

A: Prompt Cache is matching unintended content. Solution: Add a unique identifier or timestamp to prompts to force cache miss: {prompt} [request_id: {Date.now()}].

Q: "WebRTC shows my real IP despite using proxy"

A: WebRTC bypasses proxy for peer connections. Solution: Completely disable WebRTC in browser settings or use WebRTC Control extension to block STUN requests.

Q: "Account suddenly requires phone verification"

A: Triggered by IP change, new device login, or suspicious activity. Solution: Use real physical SIM verification service, bind 2FA immediately after verification to prevent re-prompts.