Add user to parent folder + sub folders

I'm trying to add an internal user within my organization to a 'parent' folder so that they can access both this folder, and all subfolders within this folder. When I invite them, I get a notification that they were successfully invited. However, they are still not able to access the parent folder (or sub folders). It will be very time consuming to have to manually add them to every single sub folder, so any help is greatly appreciated. Thank you!