Note: You only need this if you want to sell user subscriptions online. In other words, only install this if you want to sell access to a particular user group (in Joomla!), or role (in Wordpress). You do NOT need this for recurring payments to work (nor do you need to mark your products as being subscriptions).
This is NOT an nBill extension and cannot be installed using the nBill extension installer, it is a plugin that must be installed using the appropriate Joomla installer OR (in the case of Wordpress 4.x), must be unzipped and uploaded to your site's wp-content/plugins directory. Note that the same download can be used on both Joomla! and Wordpress. This plugin is released under the GPL v2 license. nBill itself is released under its own license.