The full version of FL Studio 20 can be unlocked in different ways, but unlocking through a registry file known as a regkey is arguably the most.
Browse to the saved 'FLRegkey.Reg' file, select it and accept. On the ‘About’ pop-up enter your account email and password then click ‘ Unlock with file ’. Unlock/update FL Studio - Open FL Studio and from the top-left menus select 'HELP' (or '?' In FL Studio 12) then 'About.', at the bottom of the list.