使用Cookie PHP时出现未定义的错误

Question

I have three pages: index.php, config.php, test.php.

I'm trying to grab a value from a saved cookie $_COOKIES['ID'], although when I'm on the index.php and I use file_get_contents to grab test.php, I get the error of:

Notice: Undefined index: id

But when I go to the page itself myurl.com/files/test.php, the cookie shows.

In index.php my code is:

<?php
include "files/config.php";
echo $template;
?>

In files/test.php, I'm trying to grab a saved cookie

<?php
include "config.php";
echo $_COOKIES['ID'];
?>

config.php

<?php
$template = file_get_contents('files/test.php');

$keywords = array
(
    //Site details
    "{TITLE}" => 'Hello',
);


foreach($keywords as $search => $data){
    $template = str_replace($search, $data, $template);
}
?>