An error ocurred during installation No manager for installer unknown! What is going on? Thanks!
You have to contact the developer for help. We (itch.io) don't manage how they distribute their game, we only give them the tools to do it. If they were giving our Steam keys or anything else then that's something you'll have to talk to them about.
As always, if you paid money for something but didn't get what was advertised then contact support and we can process a refund: https://itch.io/support
Whoops, I just looked again and noticed that the creator is only selling a Steam key. That's not normally allowed on Itch. I'll let an admin know.
Edit: in the mean time, feel free to contact support and request a refund if you bought the game within the last 7 days.
P.S. Just to make absolutely certain, you mean this game, right?
the key is real but how the developer give away the file might depent how he did it. It is only a text file but might also be a bad key since Valve stops developers from giving away many keys and developers could remove people key even after they submitted.
This is why only selling keys are not allow, your game could be taken away.
I'm afraid that's hard to say now. You really ought to contact the developer. Their Twitter account looks abandoned, or at least dormant, but they have a site and an e-mail address. And they seem to be known as the current maintainer of the Vulture GUI for Nethack. Thought it was a mistake at first, but it looks legit.