Idempotency keys on every operation that moves money
A caller-supplied key with a unique index turns every retry, refresh and double-click into a no-op. The single most valuable column in a payments schema.
Tagged “idempotency”
3 entries
Credit a deposit exactly once, however many callbacks arrive
A unique index on your own reference turns duplicate callbacks, browser refreshes and manual replays into no-ops instead of free balance.
Handle an offerwall postback without paying twice
Signature check, unique constraint, credit inside a transaction. Networks retry postbacks, so the same completion will arrive more than once.