Preventing a customer from answering the same survey more than once

​@Aine,

You can create a mailing list where the ExternalDataReference is the voucher number. When someone completes the survey add the contact (voucher number) to the list.  At the beginning of the survey add automatic validation against that list based on ExternalDataReference and screen-out anyone that validates. Anyone else would continue with the survey.

Turn off ‘Prevent Ballot Box Stuffing’. 

Hi ​@TomG 

Excuse me for my beginner's questions... Do you decide to set up a contact list like the one we have here?
And then what you are talking about:

At the beginning of the survey add automatic validation against that list based on ExternalDataReference and filter out anyone who validates. Anyone else would continue with the survey.

It is added in a validation here in the survey flow? how would it be done?

Thank you for your explication

​@TomG  perfect thank you very much for the clarifications ...
When you talk about Authenticator and End of Survey, you are referring to 
You are referring to these elements that I show in the picture, is true?

Yes, that’s what I’m referring to.  Except, the Authenticator acts like a branch, so the End of Survey element should be indented under it.

ahh perfect! ... just as I show you

Thank you! Very much