I'm not sure what you mean by "add a steam key"? Add it to what? To itch? Or do you mean sell a steam key to you?
Ah, I see. Thanks for clarifying. It's actually not available for sale on itch, yet. I just use itch for communications. It's available directly on steam or on my Patreon. Or if for some reason, you can't use those paths, but would still like to purchase, let me know and I'll figure something out for you. Thanks.