Just for precision since we had a lot of questions around that, buying the early access will grant you access to all future updates there will be no extra cost to have the full game.
Hi,
If you already had alpha access you received the exact same key for the beta version so if you already activated it on your account it will say duplicate.
If you never received any key until this key and it says duplicate send me a mail at [email protected] with your backer details thanks!