Populating a Field via a Querystring

You can populate a field with data from a querystring by setting the default value of a field to be the be the key of your querystring.

This will set the value of the field to whatever the key equals in the querystring in your URL.

Pre-selection a list item via a querystring

To accomplish this, the key needs to be the field key for the list and the value needs to be one of the list values.

Using data from a Submission as Querystring data in a redirect

You can create a redirect action that contains a merge tag from the form as part of the URL. use-merge-tags-in-a-redirect