The Key That Expired

A reconciler sweeps for payout rows still marked pending and retries each one against Stripe, reusing the idempotency key stored on the row. It runs nightly at 02:00. One merchant is paid twice: the original request at 01:40 returned a 500, and the sweep at 02:00 the following night resent it with the same key.

What explains the duplicate?

The key exceeded the 255 character limit and was truncated, colliding with a different payout's key.

Keys are only retained for about 24 hours. Once the original is pruned, a request carrying that key is treated as brand new, so the retry created a second payout.

A 500 means the request never reached the endpoint, so nothing was stored under the key. The retry made the first real payout and the duplicate came from somewhere else.

Keys are scoped per API version. The reconciler pinned a different version from the service that made the original call, so the two requests never shared a key namespace.