It seems the key is region restricted, as it won't activate on my steam account (EU).
( https://www.steamgifts.com/discussion/rtVEQ/humble-bundle-april-2021-humble-choice-17 )
So you should propably reroll this giveaway, or delete it and create a new one for your region.
Thanks anyway for the chance and I hope the new winner will enjoy the game. :)