I have uploaded another version with the code modified, now the problem is gone. However there are other plugins throwing issues as well, when I try to open the preview window:
Fatal error: Call to undefined function wc_is_21x() in /homepages/41/d83849780/htdocs/airtorque_wp/wp-content/plugins/woocommerce-catalog-visibility-options/classes/class-wc-catalog-visibility-options.php on line 27
It says that the Woocommerce Catalog plugin has errors in it, but I highly doubt that's possible. I'm suspecting, that some other plugin is causing these issues. There are many more errors, they are just not visible, because the ajax requests are terminated by the first fatal error.
One of your plugins or the theme is malfunctioning, because these errors should not happen. Try to disable all the plugins and enable them one by one to determine which is causing the fatal errors.
Plugins like: “security, caching, minification, site under construction” are tend to cause these issues, I suggest you try to disable them first, then see what happens.Best,
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