While version 1.35 is an older build, using a legitimate key via

Go to your Library > Euro Truck Simulator 2 > Install.

Open > Games > Activate a Product on Steam... > Enter your code. Legacy (Non-Steam)

You can obtain a legitimate product key through several official and verified channels:

: For keys purchased on Steam or through bundles from sites like Humble Bundle , open the Steam client, navigate to Games > Activate a Product on Steam , and enter your code. Legacy/Retail Activation