Hey there,
I am sorry to hear it not working as intended. The files should be able to be a new project. It does not work (in my experience to add it to an existing project). This is why in the documentation I think I wrote a few lines about migration of some blueprints. I never tried to migrate the entire folder. It should work with you going through and migrating each asset(or subfolder) individually Asset Actions > Migrate
You bought this on FAB right? It is sadly In epics hands for migration to work. If you are unable to get it working within epics with the asset action feel free to refund it. But I hope I was able to help :)