private function executeRequest($method, array $fields)
 {
     $currency = WPAM_MoneyHelper::getCurrencyCode();
     $fields = array_merge($fields, array('USER' => $this->apiUser, 'PWD' => $this->apiPassword, 'VERSION' => '65.0', 'SIGNATURE' => $this->apiSignature, 'METHOD' => $method, 'CURRENCYCODE' => $currency));
     WPAM_Logger::log_debug('PayPal MassPay post data:');
     WPAM_Logger::log_debug_array($fields);
     $postData = http_build_query($fields, NULL, '&');
     $response = $this->executePayPalRequest($postData);
     WPAM_Logger::log_debug('PayPal MassPay response:');
     WPAM_Logger::log_debug_array($response);
     return new WPAM_PayPal_Response($response);
 }