The prepopulate app does not work

This is a terrible explanation! and does not help to guide at all. Also https://prepopulate.jotform.io/ does not work.

I presumed you have issues with prepopulating your form. Would you mind sharing with us the URL of the form in question and which fields you'd like to prepopulate? We can help do it.

Also, the Prepopulate App worked for me. There is likely an error to your end, so I'd appreciate it if you can check that for us. You only need to open your browser console to do so, guide below:

https://www.jotform.com/help/453-How-to-get-a-console-report-from-most-common-browsers

Kindly take a screenshot if there are errors in red lines, and kindly access this thread and upload the screenshot.

Guide to upload screenshot: https://www.jotform.com/help/438-How-to-Post-Screenshots-to-Our-Support-Forum.

In the meantime, check the app through your other browsers.