code: private function _convertRegisterDestination($request) {
  
          $parameters = array();
          $parameters['Action'] = 'RegisterDestination';
          if ($request->isSetSellerId()) {
              $parameters['SellerId'] =  $request->getSellerId();
          }
          if ($request->isSetMWSAuthToken()) {
              $parameters['MWSAuthToken'] =  $request->getMWSAuthToken();
          }
          if ($request->isSetMarketplaceId()) {
              $parameters['MarketplaceId'] =  $request->getMarketplaceId();
          }
          if ($request->isSetDestination()) {
              $DestinationRegisterDestinationInput = $request->getDestination();
              foreach  ($DestinationRegisterDestinationInput->getDeliveryChannel() as $DeliveryChannelDestinationIndex => $DeliveryChannelDestination) {
                  $parameters['Destination' . '.' . 'DeliveryChannel' . '.'  . ($DeliveryChannelDestinationIndex + 1)] =  $DeliveryChannelDestination;
              }
          }
  
          return $parameters;
      }
docs: Convert RegisterDestinationInput to name value pairs