Thanks for writing in! Are you referring the site that I have added into the secure note below ?
First you can try validating your site by disabling your child theme. To do that, you can activate your parent theme and then try to validate.
If you’re still having issues, disable all of your 3rd party plugins and see if you can validate your site.
Most common issues are that you may have not enabled PHP cURL extension on your server which is a requirement. Also make sure to use a PHP version like v5.6.x or later to avoid incompatibility issues. We also have a troubleshooting guide available here (https://theme.co/apex/forum/t/troubleshooting-validation-connection-issues/201).
In case if you cannot resolve the issue, provide us with your WordPress login credentials in a secure note to check your issue further.