In shortIdempotency means that performing the same operation more than once does not change the outcome; in integration it keeps retries from producing duplicate records.
Retrying after an outage, “at least once” delivery and replaying a buffer can make the same message reach the destination more than once. If the destination action is not idempotent, the same production confirmation could be posted twice.
Common techniques: generate a unique key for the event and store it with a unique constraint at the destination, write with an “insert if absent” pattern, or use the identifiers the destination system provides to recognise repeated calls. For SQL the SQL table designer generates this pattern ready-made.
In OPC Router projects
In OPC Router workflows, duplicate behaviour is tested explicitly in acceptance: after a connection is cut and restored it is verified that the same transaction is not created twice.