SSL Certificate Expired: PKIX Validity Check Failed

What it looks like in the log

sun.security.validator.ValidatorException: PKIX path validation failed: java.security.cert.CertPathValidatorException: validity check failed

How to fix it

1. Verify your computer's date, time, and time zone in your operating system settings, enable 'Set time automatically', and click 'Sync now'—an incorrect local date (such as a clock set in the past or future) will make valid certificates appear expired.
2. If you are using a third-party launcher like HMCL, open the launcher's Download settings and switch the download provider/mirror (for example, between Official and BMCLAPI) to bypass a server with an expired certificate.
3. Update your launcher and Java runtime to the latest release so Java's built-in root certificate store (cacerts) includes current certificate authorities.
4. Disable HTTPS/SSL scanning in third-party antivirus software or local proxies/VPNs that inject their own local certificates, as an expired proxy certificate will trigger the same error.
5. If only a specific launcher help page or update check fails while your system clock is accurate, the remote website's SSL certificate has expired on the host's end; manually download launcher updates from its official GitHub Releases page until the maintainers renew their domain certificate.

Check your own log