The error can occur due to various reasons:

This document outlines the common causes and solutions for the error message: "Steam API has failed to initialize" when attempting to launch Assetto Corsa. This error indicates that the game executable cannot establish a connection with the Steam client, preventing the game from verifying ownership and launching.

Ensure it is set to (or the correct numerical ID for Assetto Corsa, which is 244210 ). There is often a button next to the list to reset or auto-detect this. 3. Check Windows Firewall and Antivirus

Your security software may be blocking the game's attempt to access the Steam API. Open settings.