SSL Certificate Expired or System Clock Wrong (CertPathValidatorException: validity check failed)

What it looks like in the log

java.security.cert.CertPathValidatorException: validity check failed

How to fix it

1. Open your operating system's Date & Time settings, verify the year, month, day, and time zone are accurate, enable 'Set time automatically', and click 'Sync now'.
2. If you are using a third-party launcher like HMCL or Prism Launcher, go into the launcher's download settings and switch the download provider/mirror (for example, between Official and BMCLAPI) in case one server's SSL certificate has expired.
3. Update the Java runtime used by your launcher or game to a current build of Java 17 or Java 21 so that its built-in root certificate store (`cacerts`) is up to date.
4. Disable HTTPS/SSL scanning in any third-party antivirus, firewall, or local proxy tool that may be intercepting connections with an expired local certificate.
5. If your system clock is correct and only a specific launcher update check or help page fails, wait for the website maintainers to renew their server's expired SSL certificate or manually download the latest launcher version from its official GitHub releases page.

Check your own log