An unexpected application error occurred: sun.security.validator.ValidatorException: PKIX path building failed. sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certifification path to requested target.
While the error sounds like it SLL certificate related. In most cases it's not. If the error occurs when trying to apply the license key. There is a good chance that it's related to your java version.
TruOI/iDashboards is in the process of moving away from using license files to using license keys.
License keys are more convenient. If you are renewing or making changes to your license. The changes are made on our license server and all you should need to do is refresh the key using the update license button in the admin console
To resolve the error you'll need to update Java. It's recommended that you upgrade to iDashboards version 12. Which support will upgrade Java to version 17 and Tomcat to version 10.
This should allow you to apply the key. However support is still investigating the issue. The verbiage of the error might be different and require a different solution.