RateProblem records how the calling member rates the problem, from 1 (bad) to 5 (good) stars, and returns the problem's updated rating, the same one DescribeProblem reports in Problem.rating. It sets an absolute state, not a toggle: the stars and comment sent replace the member's previous rating, and 0 stars withdraws it. The comment is optional with any number of stars; it is read only by the problem's editors, so the member cannot read it back, only replace it by rating again. Refused while the space has ratings off.