Error codes in HTTPS and how to fix them
When your browser throws a big scary error page while you’re trying to access a website, it’s usually speaking in HTTP status code language.
HTTPS (HTTP over TLS/SSL) adds encryption to the mix — which means sometimes, your errors aren’t just about the page not existing, but also about certificates, encryption handshakes, or network trust.
Think of it like a package delivery service:
- HTTP = delivering the package in plain sight.
- HTTPS = delivering it inside a locked box with a security seal. If something’s wrong with the lock, key, or box, your package (website) won’t be delivered.
1. 400 Series — Client-Side HTTPS Errors
These mean the client (browser, mobile app, API consumer) made a bad request or terminated it early.
| Code | What It Means | Common HTTPS Causes | How to Fix |
|---|---|---|---|
| 400 Bad Request | RFC 7231 §6.5.1 — Server couldn't parse the request. | Wrong headers, malformed cookies, or unsupported TLS extensions. | Clear browser cache/cookies, check request headers in DevTools, ensure TLS version compatibility. |
| 401 Unauthorized | RFC 7235 §3.1 — Missing or invalid credentials. | Expired/missing tokens sent over HTTPS. | Re-authenticate, refresh tokens, verify OAuth flows. |
| 403 Forbidden | RFC 7231 §6.5.3 — Server understood but refuses to authorize. | IP restrictions, HTTPS-origin CORS issues. | Fix permissions, update CORS policy. |
| 404 Not Found | RFC 7231 §6.5.4 — Resource doesn't exist. | Mixed content requests blocked by HTTPS. | Use HTTPS for all resources, fix broken URLs. |
| 408 Request Timeout | RFC 7231 §6.5.7 — Server timed out waiting for request. | HTTPS handshake took too long. | Optimize TLS handshake, use keep-alive. |
| 499 Client Closed Request(Nginx-specific) | Nginx docs — Client closed the connection before server response. | Browser timed out during TLS handshake or user navigated away mid-request. | Reduce server latency, optimize TLS negotiation, enable persistent connections. |
2. 500 Series — Server-Side HTTPS Errors
These mean the server encountered an issue while processing the request.
| Code | What It Means | Common HTTPS Causes | How to Fix |
|---|---|---|---|
| 500 Internal Server Error | RFC 7231 §6.6.1 — Generic server failure. | Expired SSL cert, misconfigured TLS termination. | Check server logs, update/reload certs. |
| 502 Bad Gateway | RFC 7231 §6.6.3 — Proxy/gateway got invalid response from upstream. | TLS version mismatch between load balancer and upstream. | Match TLS versions, fix proxy SSL configs. |
| 503 Service Unavailable | RFC 7231 §6.6.4 — Server is overloaded or down. | TLS handshake failures during high load. | Scale infra, enable connection reuse. |
| 504 Gateway Timeout | RFC 7231 §6.6.5 — Upstream server didn't respond in time. | Slow backend over HTTPS. | Optimize backend, reduce handshake latency. |
3. HTTPS-Specific Certificate & Security Errors
These don't always map to HTTP status codes — browsers often block the request before HTTP even starts.
| Error | Meaning | How to Fix |
|---|---|---|
| ERR_CERT_DATE_INVALID | Certificate expired or not yet valid. | Renew with Let's Encrypt, AWS ACM, etc. |
| ERR_CERT_COMMON_NAME_INVALID | Cert domain mismatch. | Issue cert for correct domain/subdomains. |
| ERR_SSL_VERSION_OR_CIPHER_MISMATCH | TLS version/cipher not supported. | Use modern TLS config. |
| ERR_CERT_AUTHORITY_INVALID | Cert issued by untrusted CA. | Use CA-signed cert, avoid self-signed in prod. |
4. Quick Fix Checklist for HTTPS Errors
- Check Certificate — Valid, not expired, domain matches.
- Verify TLS Versions — Prefer TLS 1.2/1.3 (RFC 8446).
- Fix Mixed Content — All resources over HTTPS.
- Update Server Config — Especially reverse proxy SSL settings.
- Test with Tools — Use SSL Labs Test for weaknesses.
5. Preventing Future HTTPS Headaches
- Automate cert renewals — Let’s Encrypt cron, AWS ACM auto-renew.
- Enable HSTS (RFC 6797) — Forces HTTPS.
- Monitor uptime & cert health — Tools like Hyperlook can alert before certs expire or TLS issues appear.
🔍 Final Note:
HTTPS errors are like airport security alerts — annoying, but they protect your users. Knowing the codes and their root causes means faster debugging and fewer late-night production incidents.