Background In Part 0 we built the system that Meridian Bank already has as an existing banking system: a REST API over PostgreSQL that applies every dispute rule exactly, every time. Run the same request twice, get the same answer twice. That property of building deterministic systems and testing them out comes very …

Background Meera opens her banking app and sees a payment in her transaction history that she doesn't recognise: ₹180 to SQ *TPR HSPTLTY, four days ago. She had never heard of it. So she does the responsible thing - She opens the dispute form of her bank, picks "Unrecognised or fraudulent transaction", types …