code: public function getPrepInstructionsForSKU($request)
      {
          if (!($request instanceof FBAInboundServiceMWS_Model_GetPrepInstructionsForSKURequest)) {
              $request = new FBAInboundServiceMWS_Model_GetPrepInstructionsForSKURequest($request);
          }
          $parameters = $request->toQueryParameterArray();
          $parameters['Action'] = 'GetPrepInstructionsForSKU';
          $httpResponse = $this->_invoke($parameters);
  
          $response = FBAInboundServiceMWS_Model_GetPrepInstructionsForSKUResponse::fromXML($httpResponse['ResponseBody']);
          $response->setResponseHeaderMetadata($httpResponse['ResponseHeaderMetadata']);
          return $response;
      }
docs: Get Prep Instructions For SKU
  Returns the required prep that must be performed for a set of items, identified
  by SellerSKUs, 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_GetPrepInstructionsForSKU request or FBAInboundServiceMWS_Model_GetPrepInstructionsForSKU object itself
  @see FBAInboundServiceMWS_Model_GetPrepInstructionsForSKURequest
  @return FBAInboundServiceMWS_Model_GetPrepInstructionsForSKUResponse
  
  @throws FBAInboundServiceMWS_Exception