This is because you're using checkin24-7 FREE. The free version of checkin24-7 is limited and when the reservation form is sent the administrator receives the inquiry but must then process it manually by either replying or entering the reservation into checkin24-7. Only then the reserved period will be marked as occupied in the calendar preview.
If you wish to be able to receive online reservations, you must upgrade to either checkin24-7 PRO or PRO-COMM. All PRO accounts are free to try for the first month without obligations. You can upgrade your account type by logging into checkin24-7, then click on
My account.
Please see
the features page for other differences between PRO and FREE accounts.