code: protected function buildRequestBody(\DTS\eBaySDK\Types\BaseType $request)
      {
          if (!$request->hasAttachment()) {
              return $request->toRequestXml();
          } else {
              return $this->buildXopDocument($request).$this->buildAttachmentBody($request->attachment());
          }
      }
docs: Builds the request body string.
  
  @param \DTS\eBaySDK\Types\BaseType $request Request object containing the request information.
  
  @return string The request body.