If your ApacheBooster (Nginx and Varnish plugin for WHM) is throwing a 500 Internal Server Error, this is a simple fix which may help you.
Go to Check/Repair a Perl Script in WHM
Put this path in the field which appears:
<pre class="bbcode_code">/usr/local/cpanel/whostmgr/docroot/cgi/addon_nginx.cgi</pre>
Next, click the "CHECK" button and the problem should be resolved.