Halcyon Pay idempotency key best practices
Idempotent requests
Halcyon Pay Docs/docs.halcyonpay.com
Pass a unique Idempotency-Key header so a retried request is only executed once, even if the network fails after the charge is created.
Designing robust and predictable APIs with idempotency
Halcyon Pay Blog/halcyonpay.com
How Halcyon Pay stores the first response against a key and replays it for 24 hours, and why keys should be derived from the client request.
Handling retries and idempotency in payment systems
Increase Engineering/increase.com
A survey of key derivation strategies, including hashing the customer, amount, and currency to avoid duplicate charges under retry storms.
Idempotency-Key HTTP header field
IETF Draft/datatracker.ietf.org
The proposed standard header that lets clients express at-most-once semantics for unsafe HTTP methods across intermediaries.
What is an idempotency key and when should you use one?
Fly.io/fly.io
A practical walkthrough of adding idempotency to a checkout endpoint, with a Postgres table keyed on the request fingerprint.
Exactly-once delivery is a myth. Idempotency is the answer
Confluent/confluent.io
Why distributed systems cannot guarantee exactly-once side effects, and how idempotent consumers make duplicate delivery harmless.
Add idempotency keys to your webhook handlers
Svix/svix.com
Store processed event IDs so a redelivered webhook is acknowledged without running the handler a second time.