code: public function cancelFulfillmentOrder($request)
      {
          if (!($request instanceof FBAOutboundServiceMWS_Model_CancelFulfillmentOrderRequest)) {
              $request = new FBAOutboundServiceMWS_Model_CancelFulfillmentOrderRequest($request);
          }
          $parameters = $request->toQueryParameterArray();
          $parameters['Action'] = 'CancelFulfillmentOrder';
          $httpResponse = $this->_invoke($parameters);
  
          $response = FBAOutboundServiceMWS_Model_CancelFulfillmentOrderResponse::fromXML($httpResponse['ResponseBody']);
          $response->setResponseHeaderMetadata($httpResponse['ResponseHeaderMetadata']);
          return $response;
      }
docs: Cancel Fulfillment Order
  Request for Amazon to no longer attempt to fulfill an existing
  fulfillment order. Amazon will attempt to stop fulfillment of all
  items that haven't already shipped, but cannot guarantee success.
  Note: Items that have already shipped cannot be cancelled.
  
  @param mixed $request array of parameters for FBAOutboundServiceMWS_Model_CancelFulfillmentOrder request or FBAOutboundServiceMWS_Model_CancelFulfillmentOrder object itself
  @see FBAOutboundServiceMWS_Model_CancelFulfillmentOrderRequest
  @return FBAOutboundServiceMWS_Model_CancelFulfillmentOrderResponse
  
  @throws FBAOutboundServiceMWS_Exception