whmcsZimbraSingle/decrypt.php

<?php
    $adminPassDecrypt = localAPI('DecryptPassword', array('password2' => 'dNPmi0wk0qsIXkXKwi2dZxP1xcNYvOp/rHidfc2b'));
    if ($adminPassDecrypt['result'] == 'success') {
       echo $adminPassDecrypt['password'];
    }