It's an eight character code. I'm not overly familliar with GOG codes, but aren't they normally four groups of characters seperated by hyphens?
Gift codes are the 16 character format. Bonus codes are the 8 character ones, though they are a bit rarer. Not sure if you can only redeem some of the games, but at least you won't have to dig around for the bonus redeem page, since it's currently the same as the gift redeem one.
tl;dr Don't worry, should work fine.