Hi jj177,
I had the same problem under Linux. When installing the mod you have to move two directories from the mod folder to the main game folder (as per the installation instructions), one of which is called '.import' which under Linux is a hidden folder and has to be explicitly shown so it can be moved. I have no experience with Mac, but since it is based on Unix too, perhaps the folder is hidden for you as well. Without the links stored in this folder Godot can not properly read and link all the stuff from the mod thus making loading into the game impossible.
I hope this helps. Good luck and have fun!