I have troubleshoot your issue again and now I see the following error when trying to validate your site.
cURL error 28: connect() timed out!
You need to make sure that your PHP cURL extension is enabled on your server and functioning properly. Please follow our troubleshooting guide here (https://theme.co/apex/forum/t/troubleshooting-validation-connection-issues/201).
If you have already enabled cURL extension, try adding the following code into your child theme's functions.php file and validate your site again. I have already installed a child theme and activated it for you.
//adjustments to wp-includes/http.php timeout values to workaround slow server responses
add_filter('http_request_args', 'bal_http_request_args', 100, 1);
function bal_http_request_args($r) //called on line 237
$r['timeout'] = 15;
add_action('http_api_curl', 'bal_http_api_curl', 100, 1);
function bal_http_api_curl($handle) //called on line 1315
curl_setopt( $handle, CURLOPT_CONNECTTIMEOUT, 15 );
curl_setopt( $handle, CURLOPT_TIMEOUT, 15 );
Let us know how it goes.