If you purchased a key from a third-party reseller (like G2A, Kinguin, etc.), that key is for activating the game on Steam , not for World of Trucks. Once the game is in your Steam library, follow Method 1 above. Do not try to enter that key into WoT.
Log in with your Steam credentials. The site will automatically scan your library for Euro Truck Simulator 2 American Truck Simulator Public Profile Check: Ensure your Steam "Game Details" are set to how to create world of trucks account without product key
Some people try to use found online, but: If you purchased a key from a third-party