Go to the tab and click Verify integrity of game files... . Steam will automatically detect and redownload the missing .dll file.
— it is almost certainly a scam or malware. The correct filename is steam_api64.dll . Get it only from verified game installations or Steam itself. steamapi64rdll file download high quality
Sometimes, during a manual cleanup or uninstallation of another program, system-level files get swept away. How to Download a High-Quality, Safe Version Go to the tab and click Verify integrity of game files