Thanks for writing in! The bundled plugin Envira Gallery does not ned to be registered because we do not have any license for it. We are the ones who will be providing the updates and that is why it is not necessary to enter any license for this plugin.
Since you want to install an Addon for this plugin, you will have to buy a separate license. To know more how we have integrated this plugin and about the license, please check it out here:
Thank you for your understanding.