PHP gen Steam key

<?php

function generateRandomString($length = 25) {
    $characters = '023456789ABCDEFGHIJKLMNPQRSTUVWXYZ';
    $charactersLength = strlen($characters);
    $randomString = '';
    for ($i = 0; $i < $length; $i++) {
        $randomString .= $characters[rand(0, $charactersLength - 1)];
    }
    $str = chunk_split($randomString, 5, ' - ');
    $str = substr($str, 0, -3);
    return $str;
}
        echo generateRandomString();
        echo '<br> Cette clée peut bypass certains systemes de validation telles que ceux de G2A';