Payment gateway system design: from card tap to merchant payout

Auth, capture, settlement, ledger, webhooks, and payouts — the architecture that keeps money correct at Stripe-scale traffic without double-charging.

This piece is still being finished. Same URL when it goes live — nothing to bookmark twice.

Meanwhile, these are live

Insight

The retry storm that almost paid a merchant 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.

Insight

The callback that said `SUCCESS`

Friday, the app said Paid. Monday, 15,000 XOF was missing. The callback was named SUCCESS. That was the whole problem.

Insight

Stop shipping `isPaid: true`

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.