We had a guest make a booking for 1 person, alarm bells did ring so we asked her to confirm the amount actually staying for the weekend. She replied 2 people for the 1st night and 5 for the second night. Mmm.... how do you charge for this?
Calculate 2 guests a night + 5 guests on the second night = X and change the reservation, the subtotal you have to write is X, and after you write to the guest as you calculated.