The only way to guarantee a working activation key is to purchase the game through authorized platforms.
You can download the free demo on Steam right now to see if your PC runs it well before spending a dime. Euro Truck Simulator 2 1.40.4.8 Activation Key High Quality
Marek copied it. He opened the game client, his breath hitching as he pasted the code into the activation box. He clicked 'Submit.' The only way to guarantee a working activation