If you're getting an 'invalid key' error message when trying to activate Metal Gear Solid CD Key on Steam, here is how to activate.
First, go to this link:
On that page, simply click your region, and enter your coupon code.
The website will then return you with a Steam activation code for Metal Gear Solid Phantom Pain!
You can buy a Metal Gear Solid: Phantom Pain CD Key for Steam here at just £26.99 / €37.80:
Thanks, we hope this article was useful in helping you activate your Metal Gear Solid: Phantom Pain Steam Key.