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Platform

Idempotency

The property that repeating a request produces the same result as making it once. Essential wherever money moves.

An operation is idempotent if doing it twice has the same effect as doing it once. In billing this is not a nicety: networks time out, clients retry, and a duplicate request that charges a card twice is a real financial event.

The standard mechanism is an idempotency key supplied by the caller. The server records the key with the result of the first request and returns that stored result for any repeat, rather than performing the work again.

The same principle applies to usage ingestion, where duplicate events would inflate an invoice, and to webhook consumers, which must expect redelivery.

Related terms

  • Webhook An HTTP callback sent when something happens, so your systems learn about a billing event without polling for it.
  • Metered billing Collecting usage events during a period and rating them into invoice lines when the period closes.
  • Invoice The document that states what a customer owes for a period, line by line, with tax and totals.