$txt = "<?xml version='1.0' encoding='utf-8'?>
<transactions_response>
  <data>
    <trx>
      <msisdn/>
      <product_type>GAME</product_type>
      <management_code>838873402</management_code>
      <voucher_code>QV9TP-B0UIF-VGU3O-1G0Z1-S3PT7</voucher_code>
      <serial_number>6113420739</serial_number>
      <voucher_password/>
      <pin/>
    </trx>
  </data>
</transactions_response>";
$xml_res = simplexml_load_string($txt) or die("Format Salah");
echo "<br><pre>";
print_r($xml_res);
$xml_res = (array)$xml_res;
$xml_res = (array)$xml_res['data']->trx;
print_r($xml_res['voucher_code']);
print_r($xml_res['voucher_password']);