If you purchased the software through the Fade In website, your registration key would have been sent to you in an email with the subject "Fade In Professional Screenwriting Software user information", along with your username and personalized download link. (If you purchased the software elsewhere, such as the Mac App Store, you won't have a registration key.)
Please check that you still have access to the purchasing email account to which the information would have been sent.
(Note that some email services like Gmail do not by default delete emails unless you do so specifically, so past emails are usually easy to find by searching.)
The email with your download and registration is important. Please keep it safe as you would any other purchase.Tags: download, full version, registration