Install the multiplayer files through the launcher interface.
If the fix is not built-in, copy the files from the "Fix Repair" folder into the game directory to overwrite existing files. How to Start a Session My Summer Car Cracked Multiplayer
A system that "locks" car parts once they are bolted by any player, preventing the common bug where already-bolted parts detach or disappear for others. Install the multiplayer files through the launcher interface