I´m trying to capture the value of id by using the URL, but always while printing tha array for debug its null

if ($_SERVER[“REQUEST_METHOD”] == “POST”) {

 $user_id = isset($_GET['id']);

 echo '<pre>';    
 print_r($_GET);
 echo '</pre>';

if ($conn === false) {
    die("Error");
}

if ($user_id === null) {
    echo "<script>
            Swal.fire({ 
                title: 'Invalid Request', 
                text: 'No user ID specified.', 
                icon: 'error', 
                button: 'Close' 
            }).then(function() {
                window.location = '...';
            });
        </script>";
} else {

I tried using the get variable for this