You just made a simple use case scenario, which is great. But we also need to cater for user validation, errors like inadequate funds based on the rates, inadequate exchange offering (limits) and how you would deal with that. I’m trying to start with a design that is simple and we can always add features and more user-friendliness later.
Regarding backend integration, just think about printing a receipt, tracking stock, financial administration etc. Once you have more than a handful customers a day or you have personnel not trained in cryptocoins you will need pay terminals which integrate all the above mentioned services and just a phone would be inadequate in most occasions. Just to clarify I’m talking the merchant side of things. For the consumer a phone with the App would be perfect.
