Designing scalable fintech systemsNot published yet
Scale is not a bigger Postgres cluster. It is clear money boundaries, idempotent commands, and a ledger finance can reason about under pressure.
This piece is still being finished. Same URL when it goes live — nothing to bookmark twice.
Thursday 16:47. A merchant payout. The client timed out, then fired again. Then again. Ninety seconds from paying the same person three times.
Friday, the app said Paid. Monday, 15,000 XOF was missing. The callback was named SUCCESS. That was the whole problem.
Most payment bugs are vocabulary bugs. Accepted is not confirmed. Confirmed is not settled. The three-state model this blog starts from — and why your boolean is lying to finance.
