Dishonored DLC error.

Yes, that happens because of the regions. If you check the Steam Discussions for this game, many people have that issue. Check your account details (https://store.steampowered.com/account/) to find out your version of Dishonored (for example, mine is Dishonored WW. "WW" = Worldwide).

Probably you will have to buy the DLC from somewhere else, or simply ask your friend to buy it for you and do a trade with him...

Same happened to me in the summer. I got the game from GetLoaded, and bought 3 of the DLCs from the store myself. Turned out that my region-free base game was not compatible with the region locked DLCs, which is bullshit, but it doesn't seem to bother Bethesda at all. I asked for a refund from Steam's support and they did it (to the Steam Wallet of course), and I asked someone from the US and A to get it for me instead. That worked out alright for me, I think you should opt for something similar.

There's supposedly another way which involves asking Bethesda and Steam to work together and change your game's region for something that would let the DLC to be activated for, but I've seen someone's thread somewhere who had that shit going on for long months before they stopped pointing their fingers at each other and one of them actually fixed it already. So yeah, tell your friend to ask for a refund.

I got a WW version of dishonored (from nuveem).
Do you know if the american amazon gives WW version of the DLC?