Where does the error occur?
Before a browser can send an HTTP request over HTTPS, it must establish a TLS session with the server. If the protocol, certificate or intermediary proxy prevents a valid handshake, Chrome may show ERR_SSL_PROTOCOL_ERROR.
First distinguish one website from all websites
- Check other HTTPS websites.
- If only one domain fails, use the website checker.
- If many HTTPS websites fail, check your device clock, VPN, workplace proxy, HTTPS inspection and public Wi-Fi login.
If you own the website
Verify that port 443 actually speaks TLS and the reverse proxy uses the right protocol to the origin. Then check the certificate, chain, hostname and supported TLS versions.
It is not the same as an expired certificate
NET::ERR_CERT_DATE_INVALID is a more specific time-validity error. ERR_SSL_PROTOCOL_ERROR is a broader TLS issue.
VPN, antivirus and HTTPS inspection
Intermediary security software may terminate TLS and establish a new connection. In a managed workplace, do not remove your organization's certificates; report the issue to the administrator.
What should you avoid?
Do not disable certificate validation or bypass security warnings on login or payment pages just to access a website.
Frequently asked questions
Does ERR_SSL_PROTOCOL_ERROR mean the certificate expired?
Not necessarily. An incorrect TLS endpoint, proxy or incompatible configuration can also cause it.
Can a VPN cause the error?
Yes. A VPN or proxy can change the TLS path and its handling.
Is it safe to disable certificate checks?
No. That removes important security protection.