If you recently installed the game or a repack, your antivirus (like Windows Defender or AVG) may have flagged the steam_api.dll as a "false positive" and quarantined it. Open your antivirus software's Quarantine Protection History steam_api.dll and select Important:
is highly risky and generally discouraged. This specific file is a core component of the Steamworks API, and requests for individual DLL links are almost exclusively associated with bypassing digital rights management (DRM) or "cracking" the game. steamapidll for grid autosport link