So, I am trying to insert a file with a php include, but for some reason it doesn\'t work with the full URL.
This works:
include is meant to include and evaluate a specified PHP file. If you fetch it locally, it can be processed like PHP - if you fetch it through a full URL, you will get the resulting HTML (in theory ... you may get only an error).
Supporting Docs
include 'menu.php' //Internally process a PHP file to generate HTML
or
file_get_contents('http://domainname.com/menu.php'); //Fetch resutling HTML