First Temporary "Job"

Hi everyone, I landed my first big project a week ago. I work on my own, but there’s someone acting as an intermediary between me and the client (he knows a lot more about programming than I do).

So, the way it works is that I don’t communicate with the client directly; instead, he sends me all the necessary data and reviews my code. So here’s what’s making me wary: this project doesn’t have a fixed payment. That means I’ll get paid a percentage of the work only once there are results. I understand that this is my first major project and actually my first commission ever and that I’ll be able to gain a lot of experience, but I’d like to clear up my doubts.

Should I do something about it, or should I just keep working?