code: public function getPrepInstructionsForASIN($request)
      {
          if (!($request instanceof FBAInboundServiceMWS_Model_GetPrepInstructionsForASINRequest)) {
              $request = new FBAInboundServiceMWS_Model_GetPrepInstructionsForASINRequest($request);
          }
          $parameters = $request->toQueryParameterArray();
          $parameters['Action'] = 'GetPrepInstructionsForASIN';
          $httpResponse = $this->_invoke($parameters);
  
          $response = FBAInboundServiceMWS_Model_GetPrepInstructionsForASINResponse::fromXML($httpResponse['ResponseBody']);
          $response->setResponseHeaderMetadata($httpResponse['ResponseHeaderMetadata']);
          return $response;
      }
docs: Get Prep Instructions For ASIN
  Returns the required prep that must be performed for a set of items, identified
  by ASINs, that will be sent to Amazon. It returns guidance for the seller
  on how to prepare the items to be sent in to Amazon's Fulfillment Centers, and
  identifies the labeling required for the items, and gives the seller a list
  of additional required prep that must be performed.
  
  @param mixed $request array of parameters for FBAInboundServiceMWS_Model_GetPrepInstructionsForASIN request or FBAInboundServiceMWS_Model_GetPrepInstructionsForASIN object itself
  @see FBAInboundServiceMWS_Model_GetPrepInstructionsForASINRequest
  @return FBAInboundServiceMWS_Model_GetPrepInstructionsForASINResponse
  
  @throws FBAInboundServiceMWS_Exception