Synty in UEFN

I own a few Synty packages purchased as a single developer from the Synty store.
I have experienced a few issues getting them imported into UEFN, but have gotten some to work.

Main question, are there any restrictions from using Synty assets to develop Fortnite islands? My license is for a single developer (which I am).

I do not want to do anything that might get a ban.