# MESH API question about LocalId
**URL:** https://openhealthhub.org/t/mesh-api-question-about-localid/2350
**Category:** NHS Spine & APIs Support
**Created:** [26 January 2021 11:26 UTC](https://openhealthhub.org/t/mesh-api-question-about-localid/2350 "2021-01-26T11:26:47Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@kkusnadi](https://openhealthhub.org/u/kkusnadi)
#### Post date: [26 January 2021 11:26 UTC](https://openhealthhub.org/t/mesh-api-question-about-localid/2350/1 "2021-01-26T11:26:47Z")
Hi, everyone
I have a question about LocalId in the control (.ctl) in the MESH specification … what this element signifies… is this one need to be associated with the processing node or per ODS (or even per mailbox) ??
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### Author:  [@mayfield.g.kev](https://openhealthhub.org/u/mayfield.g.kev)
#### Post date: [26 January 2021 11:52 UTC](https://openhealthhub.org/t/mesh-api-question-about-localid/2350/2 "2021-01-26T11:52:53Z")
Do you have a link to an example file?
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### Author:  [@kkusnadi](https://openhealthhub.org/u/kkusnadi)
#### Post date: [26 January 2021 12:00 UTC](https://openhealthhub.org/t/mesh-api-question-about-localid/2350/3 "2021-01-26T12:00:03Z")
HI, here is the example page [Message Exchange for Social Care and Health: client user guide - NHS Digital](https://digital.nhs.uk/services/message-exchange-for-social-care-and-health-mesh/mesh-guidance-hub/client-user-guide). In fact, I found out the answer when looking the example you have asked… it seems this field is up to the implementer what they choose to link with. The `` section is an optional field. You can specify any reference or information which is useful to you, such as which clinician sent the file. You may leave blank if you wish.
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### Author:  [@Pedros](https://openhealthhub.org/u/Pedros)
#### Post date: [26 January 2021 17:08 UTC](https://openhealthhub.org/t/mesh-api-question-about-localid/2350/4 "2021-01-26T17:08:30Z")
We populate the locaID with the transaction reference number recorded in our logging system. I see you are talking about CTL files so assume you are using the MESH client. You may want to match up a CTL file with a an audit trail on a transaction in case of any errors to enable you to trace the source of the error or similar - use the locaID to do that
Hope that helps?
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### Author:  [@kkusnadi](https://openhealthhub.org/u/kkusnadi)
#### Post date: [26 January 2021 17:16 UTC](https://openhealthhub.org/t/mesh-api-question-about-localid/2350/5 "2021-01-26T17:16:17Z")
Thanks for the information @Pedros . Actually we implement MESH API… so this should be under Mex-LocalId,
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### Author:  [@Pedros](https://openhealthhub.org/u/Pedros)
#### Post date: [26 January 2021 17:26 UTC](https://openhealthhub.org/t/mesh-api-question-about-localid/2350/6 "2021-01-26T17:26:53Z")
Yep. We use the API too, so use Mex-LocalID for your transaction number or similar in the API message header