PHP file not executing Python file from webserver

Question

I'm currently working on a project with multiple raspberry's which are all controlled by a main panel on a webpage. The idea is that if I press a button on the webpage it runs a Python script on the pi which is connected to that certain button. It works fine, except for one pi.

I used the same code as the other pis but it won't work for some reason. Could anyone help me out?

PHP file:

<?php
system("python /home/pi/Desktop/controllers/slaap-all-off.py");
?>

JS code connected to the button calling the php file in the background:

$('#dosometing').on('click', function() {
    $.ajax({
        url : 'http://webserverip/dosomething.php'
    }).done(function(data) {
        console.log(data);
    });
});

if I run the php file on the raspberry it self it will give a reaction, however if I open the file in a webpage it won't do anything.

I think it is somewhere in the permission settings of my pi.

Does someone have any ideas?