...
Send the POST REQUEST : ( code depending on the PHP framework you use )
$transmit $transmit = array('MerchantID' => $paymentRequest->getMerchantID(), 'Len' => $len, 'Data' => $data);
$request = Request::factory($paymentRequest->getUrl()) ->headers('Content-type', 'application/x-www-form-urlencoded; charset=UTF-8')
->method(Request::POST)
→post($transmit);
...