# MESH API question about LocalId **Category:** [NHS Spine & APIs Support](https://openhealthhub.org/c/nhs-spine/25) **Created:** 2021-01-26 11:26 UTC **Views:** 1049 **Replies:** 5 **URL:** https://openhealthhub.org/t/mesh-api-question-about-localid/2350 --- ## Post #1 by @kkusnadi 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) ?? --- ## Post #2 by @mayfield.g.kev Do you have a link to an example file? --- ## Post #3 by @kkusnadi HI, here is the example page 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. --- ## Post #4 by @Pedros 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? --- ## Post #5 by @kkusnadi Thanks for the information @Pedros . Actually we implement MESH API.. so this should be under Mex-LocalId, --- ## Post #6 by @Pedros Yep. We use the API too, so use Mex-LocalID for your transaction number or similar in the API message header --- **Canonical:** https://openhealthhub.org/t/mesh-api-question-about-localid/2350 **Original content:** https://openhealthhub.org/t/mesh-api-question-about-localid/2350