The purchase code you have is for Agile theme and not of the slider. You cannot register the slider, because we have included it free of cost with the theme and since we bought the plugin.
If you want to register for the plugin support, then you will have to purchase the plugin to get the purchase code for that. Right now you can use plugin for free without having to pay for it minus the support for it. If you find any issues, we will contact the plugin author directly. Thanks!