Early Access Key is not the same as the Retail Game Key, if you have a physical copy of the game then look inside the box for a paper/card slip with a serial key on it and enter that, if you bought a digital copy then look in your in-box for any new mail from the company you purchased it from, SE/Amazon or some other digital distributor, then at the bottom of your email there should be a meteor icon (looks like the icon you use to launch the game on pc, if you have it on pc) and either click on that to reveal the code you need, or see if it is below the meteor icon.