code: protected function buildRequestBody(\DTS\eBaySDK\Types\BaseType $request)
      {
          if ($request->hasAttachment() && $request instanceof Types\UploadSiteHostedPicturesRequestType) {
              return $this->buildMultipartFormDataXMLPayload($request).$this->buildMultipartFormDataFilePayload($request->PictureName, $request->attachment());
          } else {
              return parent::buildRequestBody($request);
          }
      }
docs: Builds the request body string.
  
  @param \DTS\eBaySDK\Types\BaseType $request Request object containing the request information.
  
  @return string The request body.