Got the Steam email today. Entered the key and downloaded. Logged into game but could not link my Bohemia International account as it states I should in the Email. The button appears in the options menu but clicking it does nothing besides make a noise. What am i doing wrong?

My Steam username. Which is not the same as my BI username. I also tried doing it through the Account Linking options here and got the "game is already linked to another account" reply.