Fintech Lab
Lesson 5State and lifecycleIntermediate
The refund
Why 'just delete the transaction' is the most expensive mistake.

Yesterday a user deposited ₦10,000 via card. Today they want a refund. Junior engineers reach for DELETE. Real ledgers add a counter-entry that reverses the original without erasing it. Your audit trail must be immutable. Watch how the books unwind without losing a single line of history.

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Fintech Lab is a free, interactive lab for fintech engineers. Real ledger, your own sandbox, engineering patterns from production. See all 85 lessons.

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