I want to know if there are any additional charges for using the app.

ゲスト予約:Guest Reservations 外部サイト予約(一休.com/Expedia等):Booking site reservations(Ikyu.com Expedia and more) オーナー予約:Owner Reservations ギフト予約:Gift Reservations THE KEY予約:THE KEY Reservations DAO利用:DAOReservations

App usage is free.