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Core principle

For financial operations (/sale, /refund), treat transport failures as "state unknown" until proven otherwise.

  • Do not assume failure on timeout.
  • Use the same documentExtID for retries of the same business operation.
  • Always send and persist your own unique documentExtID per operation.

Practical default for /sale and /refund: resend the same request with the same documentExtID. The server-side idempotency logic will either return an existing result or continue processing the same operation.