Why "just retry" creates duplicate payments, and a PostgreSQL-backed design for idempotency keys that survives double clicks, timeouts, crashes and concurrent retries. Key takeaways Networks give you at-least-once delivery at best. Exactly-once delivery isn't achievable in general; exactly-once...
Source: [Dev.to](https://dev.to/mamareza/idempotency-keys-done-right-exactly-once-effects-over-at-least-once-networks-18fg)