You may or may not want to display a coupon input on the booking form. If you have no current promotions you can hide this input to prevent people searching for expired voucher codes.
Navigate to the settings option, and select the 'Booking Form' wizard.
This setting is found on the first tab 'Design'.
Scroll down to 'Would you like to display a coupon input on the booking form?' and toggle this option to the right to either activate or deactivate.
Click Save at the bottom of the box.