Keep in mind either of the statements occur the next day, that is the context must be considered to be in only past tense and FYI I know "to be" is for present and "to have been" is for past so kindly pls don't gimme that explanation.
Son, you were supposed to be here at 9:00 PM, what happened?
OR
Son, you were supposed to have been here at 9:00 PM, what happened?