The debit of your payment method for subsequent months applies only to long-term bookings (more than 28 nights). myroom24 tries to debit your payment method stored in the user account, 7 days before the start of the following month. If this is not possible, further attempts will be made 4 and 2 days and 1 day before the beginning of the following month.
You can find an overview of your monthly payments in your user account under the item: Reservations.
