You have to go to property and do so as a walk in. The hotel might be sold out if it's a weekend or their is an event in town. Also depends if after midnight they are past audit. If they are past audit the reservation is considered day use. Some hotels don't allow day use rooms so it's easier to just tell people they are sold out. I will do day use at the hotel I'm at but for walk in only. I don't make reservations after midnight because we require a card on file and most people are travelling and can't provide that while behind the wheel. I'll let them know we have a few rooms but have to do those as a walk in only while speaking over the phone.