We had to create MVP of a product for a startup to gather investments. The product is a mobile application that gives users functionality for scanning and purchasing products with just their phones in any local grocery store. It would interconnect to the store's accounting system, providing all relevant information about a product a user needs. And the purchase is done via credit card bound to the user’s account. It was to save a lot of client’s time and reduce lines in stores.
The difficulty was more on the internal side. The problems of gathering products’ info and synchronization were the biggest. It was not trivial as we had to support a range of accounting systems and provide users as much relevant information as competitors do and even more. So we built two web services. Our main backend system for the application, and an interlayer that talks to the first one and provides API for accounting systems to communicate. The mobile application was implemented in Swift for IOS and Java for Android devices.