You can restrict access to an event via Promo Code so only people with that code can purchase/attend it. This can be used for private, secret or pop-up events so only a certain list of people may be able to attend.
1. Log in to the Admin page with the URL extension /admin/plugs
2. Click on Events in the Dashboard or click on Events > Events
3. Click on your desired event you would like to make private
4. Click on the "Appearance" tab
5. Turn "Promo Code Required" on
6. Enter text for the page
i.e., "You must enter the pre-sale code to access this page."
7. Click the "Save" button on the top or bottom of the page