They seem to have fixed this, however. I sent in a support ticket a couple days ago (right before the weekend for them too, I guess?) and they got back to me today telling me they had resolved it. Tried the existing code shortly thereafter and it worked without issue.

Kudos to GOG support for handling this pretty promptly both in leading to the fix and the fix itself.

When do you input the code? I was buying via paypal and it looked like I was about to pay full price for it?

Thanks!

After sending a ticket on this Friday they got back to me Monday to say that all the original codes were fixed now and to try again. When I went to use my original code the quantity and discount were correct but the transaction didn't go through for some reason. Now I have no game and the code has been marked as used!

How does a discount code burn without a transaction associated with it? I'm done here!

P.s: I suspect the original codes were temporarily blocked with "quantity 0" over the weekend when it was revealed they were incorrectly giving away free games. That way they could take their weekend and have a go at it Monday without giving away any more games. All you guys praising GOG for making you go through all this BS for a $4 upgrade to a flawed game you already own should reconsider your logic.

I've forgotten exactly, but you have to redeem the code first to get the discount, then pay. There's a 'redeem code' link somewhere on the site, but I can't remember where I found it :).

Thanks for figuring this out. I had just noticed the code in my library and was wondering what to do with it.