# Concurrent transaction **URL:** \ **Category:** Developers\ **Created:** [March 17, 2025, 7:14am UTC](https://forum.dfinity.org/t/concurrent-transaction/42437 "2025-03-17T07:14:32Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Kashif](https://avatars.discourse-cdn.com/v4/letter/k/ecc23a/32.png) [@Kashif](https://forum.dfinity.org/u/Kashif)\ **Post date:** [March 17, 2025, 7:14am UTC](https://forum.dfinity.org/t/concurrent-transaction/42437/1 "2025-03-17T07:14:32Z")
Hi Team I am using the [construction APIs](https://internetcomputer.org/docs/defi/rosetta/icp_rosetta/construction_api/operations-flow#construction-api-endpoints) for generating a transaction and then submitting it on chain. I dont see any unique identifier like nonce in the payload. Hence i wanna understand how concurrent transaction are handle in ICP ---
**Author:** ![mathiasb](https://avatars.discourse-cdn.com/v4/letter/m/f475e1/32.png) [@mathiasb](https://forum.dfinity.org/u/mathiasb)\ **Post date:** [March 17, 2025, 8:43am UTC](https://forum.dfinity.org/t/concurrent-transaction/42437/2 "2025-03-17T08:43:42Z")
Hi Kashif, I’m not sure if this answers your question, but you can specify the [`created_at_time`](https://internetcomputer.org/docs/defi/rosetta/icp_rosetta/construction_api/operations-flow#payloads-request-structure) in transactions, which as defined in [the ICRC-1 standard](https://internetcomputer.org/docs/references/icrc1-standard#transaction-deduplication-) is used for transaction deduplication. I.e., if you e.g., send the same transfer twice, with the same `created_at_time` specified each time, the ledger will discard the second transaction as a duplicate. Without the `created_at_time`, no such deduplication will take place, resulting in the transaction effectively being executed twice. This is further elaborated on in [Roman’s blog post](https://mmapped.blog/posts/13-icp-ledger#tx-dedup).