This mod was made for mod manager. Use it https://github.com/TheLeonX/NSUNS4-ModManager/releases and don't forget to install moddingAPI (it will be installed automatically, but just make sure it exist in your folder, lmao).
ModdingAPI working ONLY on 1.09 version (aka latest/steam one), so update your game on latest version, if you have 1.08 or lower (you can check version on title screen).
If you have already installed moddingAPI, make sure you have installed it from mod manager (otherwise, delete it and install again).