Hello Everyone ,
I’m seeking your help to show me how I can validate on a filed to not expect Duplicated value that beaning enter from another user before .
I’m building the form with national ID number , I need to stop user from enter national Id that being entered before 
I’m sure a greet tool like kobotoolbox has this option however i can’t find it
Welcome to the community, @ebm_2! Unfortunately, KoBoToolbox does not support this feature at the moment. However, you could always do them manually once the data collection is over.
Thank you for your reply, I highly recommend you to work on this future it’s so important some times it’s not helping to remove duplicate after collecting from fields we give service while filling this forms so it’s not expected to give user options to duplicate given service towice for same person. Now I has to use other toll unfortunately 
The reason for this is that Kobotoolbox is designed to work offline as well. If User1 enters ID1 in the data and is working offline, how will User2 know that it is completed or not?
The problem can be prevented at the stage of assignment of the IDs to each user. Or if you want something that is capable of managing such cases, you can check ODK-X (https://docs.odk-x.org/).
If you want something commercial, DM me for some solutions which can be made to work with Kobotoolbox.
@ebm_2, maybe you could use this approach discussed in our other post (that exploits the dynamic data attachment feature):
