All of Payments & FintechPayments & Fintech
Cards & Money Handling
Stripe, Paystack, idempotency, rounding and not charging twice.
3 articles
Payments & Fintech7 min read
Your M-Pesa Callback Will Fire Twice: Idempotency, Retries and the 1037 Problem
Daraja callbacks are unreliable notifications, not a source of truth. Seven production failure modes, with the database constraints, pollers and parsers that make double charges structurally impossible.
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Payments & Fintech8 min read
KES, TZS and UGX: Multi-Currency Ledgers and the FX Gap Eating Your Margin
There is no single exchange rate in East Africa. Minor-unit traps, largest-remainder allocation, quote expiry, realised versus unrealised FX, and a schema that records the rate you actually transacted at.
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APIs & Integrations8 min read
Your Queue Isn't Broken: Background Jobs Need Idempotency, Not Exactly-Once
A crashed worker charged the card twice. The queue did its job: at-least-once delivery. The real fix is an idempotent handler, not exactly-once infrastructure.
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