When trying to install "South Park: The Stick of Truth" PC version, I get prompted to enter the CD key / product key that I found printed on the users manual in the DVD case. After entering the key correctly, it says "Activating Key with Steam" and then I get the error message: "Not available - Sorry but the items are not available for purchase in this country. Your purchase has been cancelled."

I already purchased the copy of the game on amazon.co.uk. I have the physical DVD disk here in front of me, all bought and payd for. I have a valid key, I would like to install the game.

What am I doing wrong?

What country are you in? What region is your computer set to? It sounds like steam thinks you are somewhere that is not the UK.

The country is Germany.

The UK version should usually work without any problem in the EMEA region. At least every other game I have purchased in the UK works.

Game is not yet out in Germany and Germany's version will be different from UK version, which is probably why steam don't allow its activation yet.