We are implementing the API after getting into enterprise.
The problem is that you cannot currently invite a guest and add them to the folder they need access to without them joining. I can do this through the web UI so it makes no sense that the API does not make a way for this to happen.
Currently you must invite the user, and then send a second api call to give them access to a folder. But only after the Guest has accepted the invite.
I should be able to set all permissions for the user on the initial invite. Currently they have access to nothing when they are added.