You can add a discount to a booking by creating an extra called Discount.
If your Extra setting is set to "Flexible" and you can add extras as needed, you can add the"Discount" extra directly in the booking.
Open the booking, click "Add extra"
Enter the name of the extra eg. Discount
Enter a negative value and this will apply a flat discount to the booking
If your Extra setting is set to "Select from list", you can set up discounts as extras as follows:
Go to Preno settings > Extras > Add an extra and label it Discount
Enter the discount you want to apply to a booking
To apply a fixed discount: Enter a negative value and leave all boxes unticked
To apply a fixed discount per night: Enter a negative value and tick "Charge by night"
To apply a percentage discount per night: Enter a negative value and tick "Charge by percentage"
Once the extra has been created, you can add the extra to a booking as needed.
Booking:
If you are wanting to apply a discount on your booking engine so guests can access these discounts when making a booking, check out these help articles here.