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
Wait, but activation keys are often tied to the platform. For example, a Steam key can only be activated through Steam, not on GOG. I should mention that each platform has its own process for activation. Maybe include steps on activation in the game