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Your LimeSurvey version: 3.28.57
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Hi Everyone!

I am designing a pre- and post- LimeSurvey and want to design the pre-survey so that it automatically generates a unique, randomly generated 4-digit Participant ID. I then want this Participant ID to be emailed to them when I sent out invitations to complete the post-survey. Then, for the post-survey I want them to use this same generated ID to be able to log in and complete the post- survey. 

However, I am quite new to LimeSurvey and am having difficulty trying to do this. Any advice or alternatives would be greatly appreciated! Also if this has already been asked if you could provide a link to the article that would also be great.
Thank you!

The problem with random 4 digit IDs is, that they are random, and not exclusive.

You could quite easily generate a 4 digit number like this:
{rand(1000,9999)}.

However, there is a chance that this process might generate the same 4 digit number more than once and you can't control it.

So what I recommend is to generate a random number and join it with the SAVEDID, which for a survey is always unique.

For the follow up survey you can then use the generated code as the token in a closed survey.

What is your exact need ?

maybe something like that: gitlab.com/SondagesPro/SurveyAccess/surveyChaining