Error guide / ERR_SSL_PROTOCOL_ERROR

ERR_SSL_PROTOCOL_ERROR error

ERR_SSL_PROTOCOL_ERROR means the browser and the server could not agree on a secure connection and the TLS handshake broke. Unlike certificate errors, this is about the protocol itself: an outdated TLS version, a misconfiguration, or a site that does not serve HTTPS at all. The page does not open at all.

What causes it

Most often the cause is in the server settings: only outdated TLS 1.0/1.1 is enabled, which browsers now block, or HTTPS is set up incorrectly. Less often an antivirus, VPN, or intercepting proxy gets in the way.

How to fix it

1. Run the SSL test below: it shows which TLS versions the server supports and whether HTTPS responds at all.
2. Enable modern protocols TLS 1.2 and TLS 1.3 on the server, and turn off legacy TLS 1.0/1.1.
3. Make sure a web server is actually listening on port 443 and the certificate is bound to the right domain.
4. On cPanel/LiteSpeed, confirm the domain has a valid certificate and reissue AutoSSL if needed.
5. If the site opens in a private window, temporarily disable extensions, antivirus, or VPN to find the culprit.
6. Clear the browser's SSL state (cache) and try another browser to rule out a local problem.

Related errors

• ERR_CERT_DATE_INVALID ERR_CERT_DATE_INVALID error
• ERR_CERT_AUTHORITY_INVALID ERR_CERT_AUTHORITY_INVALID error
• ERR_CERT_COMMON_NAME_INVALID ERR_CERT_COMMON_NAME_INVALID error
• NET::ERR_CERT_REVOKED NET::ERR_CERT_REVOKED error