code: protected function buildMultipartFormDataXMLPayload(\DTS\eBaySDK\Types\BaseType $request)
      {
          return sprintf(
              '%s%s%s',
              '--boundary'.self::CRLF,
              'Content-Disposition: form-data; name="XML Payload"'.self::CRLF.self::CRLF,
              $request->toRequestXml().self::CRLF
          );
      }
docs: Builds the XML payload part of a multipart/form-data request body.
  
  @param \DTS\eBaySDK\Types\BaseType $request Request object containing the request information.
  
  @return string The XML payload part of a multipart/form-data request body.