PHP- How to do str_shuffle make different value?

PHP- How to do str_shuffle make different values??

    $randomcode="QWERTYUIOPASDFGHJKLZXCVBNM1234567890qwertyuiopasdfghjklzxcvbnm";
$randomcode='NT'.substr(str_shuffle($str),5,8);
    echo $randomcode.'<br>';
    echo $randomcode.'<br>';

result:

NT2ZCI1qdX
NT2ZCI1qdX

How to make different values?? I want to insert it into my database.

$randomcode="QWERTYUIOPASDFGHJKLZXCVBNM1234567890qwertyuiopasdfghjklzxcvbnm";
$randomcode=substr(str_shuffle($str),5,8);

$stmt = $pdo->prepare("insert into AGEGroup (AGE) values (:age,$randomcode)");

foreach ($_POST['age'] as $age) {
    $stmt->execute([':age'=>$age]);
}

Thank you very much