Labs_underpass_p.upk -
Take the custom .upk file you downloaded and rename it exactly: Labs_Underpass_P.upk .
It allows for storing assets inside your level package, essential for functioning with the Rocket League Workshop. Labs_Underpass_P.upk
Labs_Underpass_P.upk is the underlying file for the "Underpass" Rocket League map. By replacing this specific file with a custom map file and naming it properly, you trick the game into loading your custom map instead of the standard Underpass, allowing you to play workshop maps in Freeplay. Why Use the Underpass Method? Take the custom