Reservations that have not yet been sent to the authorities can be cancelled, whether they contain guests or not. Once they have been sent to the authorities, they do not allow data editing or deletion, so they cannot be cancelled.

To cancel a reservation, you just have to go to your web control panel, reservations section, click on reservation details and turn off the send to police automatically button

Once auto-send is turned off, you can change the reservation status to cancelled.

Cancelled reservations are easy to spot as the colour changes from blue to red.