From the 3dgamestudio.com
No royalties
As owner of any Gamestudio single edition you can freely publish and distribute your applications. You don't need to pay royalties, you don't need to show credits, you don't need to ask for permission. There is only one exception. It's illegal to use Gamestudio for games that propagate genocide against a certain group, race, nation or religion existing in today's real world.
Do you want put royalty into your license?