Breaking a project into milestones is actually encouraged by many platforms because it protects both sides during longer or bigger projects. The client feels safer releasing smaller amounts as work is completed, and the freelancer gets paid progressively rather than waiting until the end. Most platforms have a milestone payment feature built in specifically for this reason, so asking for it is usually not a rule violation. Do you prefer working with milestones, or do you find a single payment at the end works better for your projects?