This project exists because I was frustrated with how the downloads work at cults3d.com and decided to invest a lot more hours to build this software than it would have taken me to download my files. But I got to learn a lot of things from it.
This software effectively acts on your behalf - requesting the orders and items and storing them to be processed in a way that is more useful for me. It also implements various caching and queues to download files and save images, descriptions and tags.
Since this works for you, you must allow it to use your logged-in session. You do need an active logged-in session; this software does not enable bypassing any security or access policies of the site. It can act as you and see and get files you can access only.
Cults use a secure token in a cookie called _session_id. You need to get that from the inspector's application tab.