You actually sent me a key, but it's from another game. This is the answer they gave me in support:

Do not mark the giveaway as received. It will cause you to have an unactivated win on your account which can lead to a suspension. I see you’ve already told the creator that the key was for a different game. You can try to work it out with them. If they cannot provide you a working key for the correct game, you would mark as not received or, if you are willing to do so, you can comment on the giveaway page agreeing to delete the giveaway. At that point, the creator can submit a ticket for deletion.

it turns out that if I mark the game as received, then I will be banned. I do not know what to do. You sent me the key to the game "Smoke and Sacrifice" They should have sent me "Bing in Wonderland"