PHP - identify user by url id

I've 3 buttons to rank my users. Admin, Member and a button to ban them. So now I wanted to identify them by their "url-id" with $_GET. But when I do that I get an error:

Parse error: syntax error, unexpected '' (T_ENCAPSED_AND_WHITESPACE),
expecting identifier (T_STRING) or variable (T_VARIABLE) or number
(T_NUM_STRING).

How can I fix that? I appreciate every help!

<?php
 include_once('connection.php');
 if (isset($_POST['ban'])) { 
  $sql = "UPDATE
          t_user_info
        SET
          user_level = 3
        WHERE 
          id = $_GET['id']";  

$query = $conn->prepare($sql);
$query ->execute(array('user_level' => $user_level));

session_unset();
session_destroy();
header('Location: /PHP/index.php?page=ban');
}
if (isset($_POST['admin_btn'])) { 
 $sql = "UPDATE
          t_user_info
        SET
          user_level  = 1
        WHERE 
          id       = $_GET['id']";  

$query = $conn->prepare($sql);
$query ->execute();
header('Location: /PHP/index.php?page=admin');

}

if (isset($_POST['member_btn'])) { 
$sql = "UPDATE
          t_user_info
        SET
          user_level  = 2
        WHERE 
          id       = $_GET['id']";   

$query = $conn->prepare($sql);
$query ->execute();
header('Location: /PHP/index.php?page=member');

}

?>