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(Write here your question/remark)Please help us help you and fill where relevant:
LimeSurvey version: Version 6.6.5
Own server or LimeSurvey Cloud: LimeSurvey Cloud
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Hi there, 

I was wondering if it is possible to upload a list of usernames on the back end of limesurvey so that if the participant enters their username incorrectly it will block them from proceeding until they enter it correctly? Ideally, all participants would get the same general link (ie. no individualized links) and then as they enter their usernames (which we are linking with another survey which is why we need this to be correct), LimeSurvey would check the entered usernames against a pre-uploaded list of valid ones.

Hope I am making sense!

Thank you very much for your help.

There is no "user administration" in Limesurvey.

However, one idea is that you use the username as token and don't send them individual links.

If the link to a closed survey doesn't contain the token, Limesurvey will ask for the token. So you could basically upload the usernames as tokens via CSV file and Limesurvey will check if this username/token exists / has been used before.