Reverse a booking (Storno)

Open Bookings and click the posted booking you want to cancel.
Find the state section with the buttons. Reverse is shown only for a booking that is already posted, and only if your role may post. A booking you have not posted yet can simply be edited.
A booking that belongs to an invoice you issued is not reversed here. Correct it through the invoice under Invoices.
Click Reverse. The app explains that a reversal dated today cancels the booking, then asks you to confirm with Book the reversal.
The original booking stays unchanged. The reversal is its own booking, and the original is then shown as Cancelled in the list.
Enter the correct booking anew afterwards, for example from the receipt in the Inbox.