The product code you've entered has already been activated by a different Steam account. This code cannot be used again. Please contact the retailer or online seller where the code was purchased for assistance.
https://i.imgur.com/NbPZYO0.png

Поменял код, попробуйте теперь

same
https://i.imgur.com/2cku9Lz.png

Поменял ещё раз ключ, пробуй снова

This one worked, thx!