installation folder to your antivirus "Exclusions" or "Whitelist" [1]. Verify Game Files (Legitimate Copies)
The error involving steam_api_ext64.dll is a specific issue typically tied to the game's interaction with Steam services or, more commonly, a failure in the game's authentication layer. Core Cause: Antivirus Interference
or other antivirus software flagging the file as a "false positive" and either quarantining or deleting it. Missing Dependencies: The system may lack the necessary Visual C++ Redistributable packages required to run 64-bit DLLs. Incorrect Installation:
When you buy Mafia 3 legally on Steam, this file is installed automatically. If it goes missing or gets corrupted, the game refuses to launch.
Users often encounter "failed to load" or "missing" errors, which prevent the game from launching.
Open your antivirus software and look for the Protection History or Quarantine section. If you see steam_api_ext64.dll , restore it.