Dear community,
I am about to build a form by Xlsx file, In this form I want to constraint anonymous users to submit the form only once without logging in with a username and password. I appreciate your help and contributions. 
Hi @alan_luqman,
You can use Online-only (once per respondent) option under the data collection section.
You can find more information on this method in this help article:
https://support.kobotoolbox.org/data_through_webforms.html#collection-settings
If you need further help, don’t hesitate to ask 
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Dear @hakan_cetinkaya
Thanks for your help. I’m already aware of this method, but I need to implement it directly within the Excel file rather than through the platform.
@alan_luqman, if that is the case then try the Dynamic Data Attachment feature as outlined in this post discussed previously:
But, please be sure that the syncing time is 5 minutes. If you try to submit a record within the 5 minutes syncing time users are able to submit another record too.
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Dear @Kal_Lam
I appreciate your help. This solution may be helpful in other cases where I have got the list of users previously. but in my case, there is no previous user list because this is the first time I have published this form to the public and a lot of anonymous users will fill this form out. So, to prevent submission duplication I need the feature to make this prevention.
@alan_luqman, there should be some variable that will check if the submission is being duplicated. The above workaround checks the name variable to see if that name already exists in the server. If it exists, then the system would be flagged out.
