This is a key from the Humble Play Pink with Twin Sails Bundle that I only purchased yesterday so it's not expired.
I've checked SteamDB, and there is no region locks on this game or key to my knowledge.
The key seems to function, as it recognizes the game rather than giving me your error message when I try to redeem it - I already owned this game for a few years, and trying to activate products you already own does not use the key up.

Are you sure you put the key in correctly and didn't miss a character?

I can try to contact Humble support and ask them if they can provide a new key, but I'm not sure what else I can do beyond that if they don't.