Change your rules for the online booking at dinnerbooking.com.
Go to Online Booking -> Global Settings

Details

- Pax allowed per booking
Controls the minimum and maximum number of guests per booking.
If a guest try to book for more than the maximum allowed, they are asked to contact the restaurant. - Cut time
Closes for new bookings during service. If service starts at 12.00, cut time Lunch can be set to 11.30.
At 11.30 all lunch times that day will then be closed, only allowing guest to book for dinner - No online bookings later than specified hours prior to arrival
Set a limit for when a booking can be made.
If set to 1 hour, and a guest want a booking for 18.00, he has to create it at 17.00 the latest. - Max days allowed in advance for booking
Controls how many days in the future the guest can book.
If set to 30, guests can only make a booking for the next 30 days. - Allow Note
Allow the guests to write notes for their booking. It could speical requests, birthdays or allergies.