Allow a link to only be completed once

My programmer has set up my surveys so that they have a unique code so we know who I sent the specific survey to and I know it is definitely their data that I get back.

Recently, an end user whom we sent the survey to, passed it on to another person to complete.  Jotform allowed them to take the survey even though it had been completed by another person.  So two people took the test that we wanted only one to take.  Then the data of the first person was overwritten by the other or the other got the data from the first person.  No matter, I understand that is how it is set up.   

My question is, can jotform identify whether someone has already taken a specific form and not allow that one to be completed by someone else.  I would expect the 2nd person trying to take it could get an error message before they are allowed to enter answers that says something like "This form has already been completed.  Please contact the organization or person who sent it to you."

Is there a way to do this?  I saw some information on unique submissions, but I don't know whether that will cover it because my users could send an email with the link to anyone.

Thanks, Caryn Lee

What is the form in question? How is the Unique Code generated or provided? We would like to understand how your programmer set this up. If the unique code is populated into a field via URL parameter, you can enable the Unique Question feature: https://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question

So, if the form is attempted to be submitted again with the same code, the system won't allow the submission.

I’ll send this to my programmer to answer. But if I used the feature you mention, they would only find out after they answered 129 questions and hit submit? Caryn
Sent from my iPhone
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That is correct. The error will be shown on submit. It is not possible to display an error when the form is loaded. I can only suggest you to add a warning message, at the top of your form using a text field, that the same code cannot be used multiple times.