Out Parameter /ref Parameter issue with PHP SOAP call

I have following web service description

public String strGetCustomerValidation (string strAppID, string strADC_TranCode, string strDelimiter, string strDate, string strTime, string strNetID, Int32 intRefNum, Int32 intSTAN, string strTranMsg, string strMerName, string strMCC, string strToken, string strCustName, string strIDNum, string strMobile, string strEmail, ref DataTable dtAccData, String R1, String R2, String R3, String R4)

And I'm using nusoap and below is my code. but gives me errors. I think it is due to ref DataTable dtAccData

How should we deal with these ref or out parameters.

$param = array(
            'strAppID'          =>  'MYAPP01',
            'strADC_TranCode'   =>  '81',
            'strDelimiter'      =>  '^',
            'strDate'           =>  $tranDate,
            'strTime'           =>  $tranTime,
            'strNetID'          =>  'WEBWS',
            'intRefNum'         =>  $txn_referance_number,
            'intSTAN'           =>  $intStan,
            'strTranMsg'        =>  '0200',
            'strMerName'        =>  'Mer01',
            'strMCC'            =>  4829,
            'strToken'          =>  $tranToken,
            'strCustName'       =>  'Cust Name',                
            'strIDNum'          =>  '1234567890',
            'strMobile'         =>  '+9432130957',
            'strEmail'          =>  'test@test.com',
            'dtAccData'         =>  '',
            'R1'                =>  '',
            'R2'                =>  '',
            'R3'                =>  '',
            'R4'                =>  ''
            );

echo '<pre>';
print_r($param);
echo '</pre>';
$getResult = $client->call('strValidateCustomer',$param);
$error = $client->getError();

Web service provider does not provide sample codes.