As stated in FAQ:
Yes! The following revenue sources are royalty-free:
- Ancillary products, including
t-shirts, CDs, plushies, action
figures and books. The exception is
items with embedded data or
information, such as QR codes, that
affect the operation of the product. - Consulting and work-for-hire services
using the engine. This applies to
architects using the engine to create
visualizations as well as consultants
receiving a development fee. - Non-interactive linear media, including movies, animated films and
cartoons distributed as video. - Cabinet-based arcade games and
amusement park rides. - Truly free games and apps (with no
associated revenue).
In other words you only pay revenue generated from UE4-powered product that user is directly interacting with
Also your comic is 100% your work right? so why you need to pay Epic for it? 