is a common issue typically caused by quarantining the file or corrupted game data . This file is critical for authenticating your game with Steam and enabling features like achievements and multiplayer. Common Causes & Solutions
He watched the folder like a hawk. The steam_api64.dll file appeared. It sat there, innocent and small.
He opened Windows Security. He went to Protection History. Sure enough, a recent threat had been quarantined.
Verifying... 100%... 1 file failed to validate and will be reacquired.