I'm running a WordPress install and was having issues with ajax-loads. Whenever I used the admin-ajax.php script, it wasn't returning anything so I decided to go to the source and see what the issue is.
It turns out that when I access the /wp-admin/admin-ajax.php file directly, it returns a 0 in the browser. I emptied the file, saved it and then tried to access it directly and it still returned a 0. I know I'm on the correct server in the correct directory as I created test files in the same DIR.
Does anyone know why this would be happening? A blank php file (with 644 permissions, and the correct owner/group) returning a 0 when navigating to it directly?
EDIT: I have highlighted a sentence above as people are skipping over that part. I have emptied the file, it still returns 0.
That file can't be accessed directly, it must be accessed through an Ajax call and you must pass in some action parameters, as in the line 28 there is a check:
// Require an action parameter
if ( empty( $_REQUEST['action'] ) )
die( '0' );
Try upgrading your installation to the latest version and check that you file size is larger than 3.75K ... If you have no cache installed than you shouldn't get a 0 from a empty php file. Do you use caching like cloudflare ?
Regarding the returned 0, try the following code:
<?php
die('Hello');
it should return a simple Hello - on my side it works, at least :)