For each ZaK booking there is an identification code formed by the initials of the booker and a progressive number. As soon as the new booking is entered, the code is generated and shown by clicking on the code you access the booking details.
You can work on the reservation by accessing the reservation detail.
So, yoiu can change the stays, register customers, register payments, add extras, issue invoices or receipts, and more.
There are several search tools for the reservations included in the property, many are in the BOOKING section, all show in the result the reservation code that allows access to detail.