Overlays from Discord, NVIDIA GeForce Experience, or Razer Cortex can interfere.
If the permissions are correct but the error remains, you might be dealing with a corrupted file. Steam provides a built-in tool to check every file in the game directory against the files on the Steam server. If a file is missing or damaged, Steam will automatically replace it. Mafia Definitive Edition Unable To Initialize Steam Api
To understand the fix, you first need to understand the problem. The is a set of protocols and tools that allows Mafia: Definitive Edition to communicate with the Steam client. This communication is critical for: Overlays from Discord, NVIDIA GeForce Experience, or Razer