Thanks for the key provided, it was valid, but there is a problem. It was for a different game, by the same name.
Seems they have allowed there to be no less than THREE games on Steam by the exact same name. And the key redeemed here was for:
https://store.steampowered.com/app/1706650/Womens_Prison/
Which my account now owns, is a different price, and doesn't seem related to the developer or publisher of the others.

What to do?