code: private function _convertGetEligibleShippingServices($request) {
  
          $parameters = array();
          $parameters['Action'] = 'GetEligibleShippingServices';
          if ($request->isSetSellerId()) {
              $parameters['SellerId'] =  $request->getSellerId();
          }
          if ($request->isSetMWSAuthToken()) {
              $parameters['MWSAuthToken'] =  $request->getMWSAuthToken();
          }
          if ($request->isSetShipmentRequestDetails()) {
              $ShipmentRequestDetailsGetEligibleShippingServicesRequest = $request->getShipmentRequestDetails();
              foreach  ($ShipmentRequestDetailsGetEligibleShippingServicesRequest->getAmazonOrderId() as $AmazonOrderIdShipmentRequestDetailsIndex => $AmazonOrderIdShipmentRequestDetails) {
                  $parameters['ShipmentRequestDetails' . '.' . 'AmazonOrderId' . '.'  . ($AmazonOrderIdShipmentRequestDetailsIndex + 1)] =  $AmazonOrderIdShipmentRequestDetails;
              }
          }
  
          return $parameters;
      }
docs: Convert GetEligibleShippingServicesRequest to name value pairs