A few years ago, I spent about a month cleaning up duplicate charges. Every service involved already had idempotency "handled": the client sends an Idempotency-Key header, we store the response under it, and if the key comes back we replay the stored response. Textbook.
Source: [Dev.to](https://dev.to/violettap/idemkit-make-any-python-operation-safe-to-retry-http-queues-functions-3335)