Maybe include steps on activation in the game. After getting the key, install Arma 2, go to the options, and there should be an option under "Game" to activate the expansion.
Let me make sure to check for any inaccuracies. For example, does Flaming Cliffs 2 require both the base game and the key? Yes. Also, maybe mention that users need Arma 2 and the Project Reality mod if that's part of the setup. But the activation key part is probably straightforward. flaming cliffs 2 activation key
Also, check if there are any recent updates to the game that might affect key activation. As of when I'm writing this, Bohemia Interactive might have updated their activation processes, but generally, it's through Steam or GOG. Maybe include steps on activation in the game