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
| Status Code | Error Message | Root Cause | Resolution |
|---|---|---|---|
| 403 Forbidden | "Access denied" | IP blocked or high-risk datacenter IP | Switch to residential proxy, clear cookies, retry after 1 hour |
| 429 Too Many Requests | "Rate limit exceeded" | Exceeded login attempts or API rate limit | Wait 15 minutes, implement exponential backoff |
| 500 Internal Server Error | "Something went wrong" | Anthropic backend issue or invalid session state | Clear all claude.ai cookies, restart browser, retry |
| Account Disabled | "Your account has been disabled" | ToS violation or payment issue | Check email for ban reason, follow appeal SOP |
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
Payment rejections occur at multiple stages. Diagnose by examining the failure point:
- Card Declined (Pre-Authorization): Insufficient balance (<$1), invalid CVV, or expired card. Ensure card has ≥$25 balance.
- BIN Rejected: High-risk prepaid BIN flagged by payment processor. Switch to credit/debit BIN from established banks.
- Address Mismatch: Billing address country/state does not align with IP geolocation. Use real US address matching proxy exit state.
- Fraud Detection: Rapid successive binding attempts. Wait 24 hours, bind only one card per session.
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.