php fedex set signature Label ADULT

[admin]

I am working on wordpress site and using woocommerce extension <a href="http://www.woothemes.com/products/fedex-shipping-module/" rel="nofollow">http://www.woothemes.com/products/fedex-shipping-module/</a>

<strong>I am Passing the values Signature value to adults. But it is not working</strong>

Please correct me where i am wrong

$request['RequestedShipment']['RateRequestTypes'] = $this->request_type;
$request['RequestedShipment']['PackageDetail'] = 'INDIVIDUAL_PACKAGES';
$request['RequestedShipment']['SpecialServicesRequested'][] = array(
    'SpecialServiceTypes' => 'SIGNATURE_OPTION',
    'SignatureOptionDetail' => array(
            'OptionType' => 'ADULT'
    )
);

`

Do i need to change something from the from the <strong>RateService_v13.wsdl</strong> file

Please suggest

Thanks