This shortcode is nearly identical to the [is_paid] and [is_free] shortcodes, except that it is for non-logged-in AND logged-in free users. Any content placed in this shortcode will only be available to users (logged-in or not) that do NOT have an active subscription. Paid users will NOT see this content.
For example:
[is_not_paid]This content is only shown to logged-out and logged-in free users[/is_not_paid]