I bought this a while back for $6 on sale.
If I add $4 will I get access to the update or do I have to buy it again for $10.
If you bought the game for $ 5, then you get all the products on this page for $ 5. Now the new version costs $ 10 and most likely it is because of this that ITCH does not allow you to download the game. Wait until the game costs $ 5 or cancel your payment and buy the game for $ 10 to receive all the latest updates on the day they are released.