Your investor did most of the work on this one by them buying the domain themselves so why would they split it with you?
We can simply call it, "Royalty Fee for the Mastermind."
Royalty for the mastermind? this is the first time I read about that term, and what made you so sure that it will get sold, why to do it yourself and make money on your own, you are trying to experiment on a method and you are trying to make it someone do it for you, if I have the idea I would it myself and if I'm successful I will sell the idea, you have not shown us a proof that you are successful on this one.