What does it mean to make up the difference for Sanya hotels snapped up by the East?

Oriental Select Sanya Hotel, which was snapped up on the spot, makes up the difference, which means adding money. In the case of booking a hotel through online group purchase, there is a room when booking online. When you check in, you are told that the reserved room is full or for other reasons, you will be asked to pay a certain price, and the staff will arrange a room with a higher grade than the reserved room.