الخطأ هنا اخى
mysqli_real_escape_sting() // string not sting
mysqli_real_escape_string() // correct
الكود الصحيح
$name = mysqli_real_escape_string($conn , $_POST['name']) ;
$email = mysqli_real_escape_string($conn , $_POST['email']) ;
$password = mysqli_real_escape_string($conn , $_POST['password']) ;
$pass = mysqli_real_escape_string($conn , $_POST['password_re']) ;