We have installed the latest version of Oxwall on multiple personal VPS servers and are experiencing the same issue as your site.  When we installed it in our shared hosting environment we noticed that the feature worked. After spending some time trying to find the differences in setup we have concluded that the feature missing from your PHP configuration is "allow_url_fopen".  This is on by default in our shared hosting environment, but not in our VPS/Dedicated environment. When we enabled allow_url_fopen on our VPS it started working!

We have gone ahead and enabled allow_url_fopen for PHP 5.6 on your server.  Please try to see if this feature is working now.

fopen -on is in the list of minimum requirements on this page.

https://developers.oxwall.com/hosting