the user interface ...

initial screen presents the list of beverages, their price and the quantities in inventory

inventory is updated after each purchase

user then chooses their payment method which will pre-authorize an amount

dispensing is done using the tap, the volume and price is measured and updated on the screen

it is possible to change selected product while dispensing

specific indicator light illuminates to indicate which tap to use depending on the selection

finally the invoice is displayed, an option to send the invoice by email is available