Error only from one country?

Check GeoDNS, CDN edge cert, or regional resolver hitting a stale anycast node.

API clients fail but browser works?

Clients may require TLS 1.2+, specific cipher, or complete chain — compare checker cipher/protocol with client logs.

Should I disable certificate validation in apps?

Never in production. Fix the chain or trust store instead.

NET::ERR_CERT_AUTHORITY_INVALID after deploy?

Almost always missing intermediate — re-bundle leaf plus vendor chain file, redeploy, and re-check within five minutes.

Guides

SSL Certificate Errors — Troubleshooting

ssl certificate error fix · certificate name mismatch · ssl troubleshooting guide

Fix common SSL errors: name mismatch, untrusted chain, expired cert, mixed content, and SNI issues using online checkers and DNS/WHOIS context.

Open SSL Certificate Checker2026-06-23

By DN01 Network Team

TLS errors surface in browsers, API clients, and monitoring probes with different messages for the same root cause. A structured checklist — hostname, dates, chain, protocol — resolves most incidents without guessing.

Start with the SSL Certificate Checker on the exact hostname users type, then cross-check DNS A/AAAA records and WHOIS if the wrong server answers.

Screenshot checker output with timestamps when escalating to hosting support — «certificate error» without SAN list evidence slows resolution.

Name mismatch (SAN/CN)

Certificate must list every hostname served — www and apex are distinct unless both in SAN.

Legacy CN-only certs fail when clients require SAN — re-issue with complete SAN list.

Multi-tenant servers need correct SNI — wrong virtual host cert produces mismatch on shared IP.

Wildcard certs cover one label level only — `*.example.com` does not cover `api.app.example.com` unless that name is listed.

Mixed content and redirects

Active HTTPS with passive HTTP assets triggers browser warnings — use HTTP Header Checker and fix asset URLs.

HTTP→HTTPS redirect loops often involve misconfigured HSTS or proxy headers — verify redirect chain separately.

Expired and date-invalid certificates

NET::ERR_CERT_DATE_INVALID means notAfter passed or notBefore is in the future — renew or fix server clock skew.

Monitoring should alert on notAfter 30/14/7 days before expiry, not only on the day browsers break.

After renewal, confirm the live edge serves the new cert — load balancers and CDNs cache old PEM files until reload.

Structured troubleshooting order

Step 1 — SSL Certificate Checker on the exact hostname users type (include www vs apex). Step 2 — Verify notAfter and full chain. Step 3 — DNS Checker for A/AAAA pointing at expected origin. Step 4 — WHOIS if a wrong server answers.

Expiry errors: renew and deploy full chain. Untrusted issuer: install intermediates. Name mismatch: re-issue with SAN covering every hostname on the vhost.

API-only failures often mean TLS version or cipher mismatch — compare negotiated protocol in checker output with client requirements.

Document resolver and timestamp when errors are geographic — CDN edge cert lag looks like random «works for me» reports until you compare checker results from multiple regions.

Frequently asked questions

Error only from one country?: Check GeoDNS, CDN edge cert, or regional resolver hitting a stale anycast node.
API clients fail but browser works?: Clients may require TLS 1.2+, specific cipher, or complete chain — compare checker cipher/protocol with client logs.
Should I disable certificate validation in apps?: Never in production. Fix the chain or trust store instead.
NET::ERR_CERT_AUTHORITY_INVALID after deploy?: Almost always missing intermediate — re-bundle leaf plus vendor chain file, redeploy, and re-check within five minutes.