Hi LEOLEE,
It depends on exactly what you are doing, but I’d suggest you check out the EULA as you may be exempt from paying royalties for your specific purposes.
I’ve bolded a section that is probably relevant from the EULA F.A.Q.:
Q. Are any revenue sources royalty-free?
A. No royalties are due on the following:
•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.
•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).
Cheers,
Michael Noland