Hi There,
Thanks for writing in! You don’t have to validate Cornerstone. If you’re prompted to do so, the most possible cause would be that you’re using an older version of X theme or Cornerstone plugin.
You can check the latest version numbers from here (https://theme.co/apex/forum/t/troubleshooting-version-compatibility/195) and then you can update your X theme by following this guide (https://theme.co/apex/forum/t/setup-updating-your-themes-and-plugins/62).
To update Cornerstone plugin, you can simply delete the current version from your WordPress plugins section and then head over to X -> Validation section, wait for few seconds to automatically install the latest version.
Once you’re fully updated, validate your X theme license and it should resolve your Cornerstone validation issue as well.
Hope that helps.