When Boozt, a leader in online retail in the Nordics, decided to migrate away from a third party payment gateway and build their own, they took the opportunity to build a new team and organization with full autonomy to create an independent system that they named Kronor. This new team took an early architecture decision: based on the transactional nature of a payment gateway, and the previous experiences of the team running large online stores, they would build most of the application logic in the database. In this talk, José Lorenzo, Director of Engineering of the Kronor initiative, will explain why they chose this architecture and its benefits, their use of statecharts to design the application logic, how they ensured the system was fully observable, and how it has proved to scale successfully in key events like the past Black Friday.