I'm trying to use a form to enable Contacts to update their preferences/contact information. I'm getting the contacts to the form by sending out an email with a link in the body that appends their ContactGUID as a query string. I then retrieve and populate the form once they open it using default values in the form example:
Default Value: {% SiteObjects.Contacts[QueryString["CGUID"].ToString()].ContactEmail #%}
This all works properly, however, once they submit the form it does not update their contact information, instead it creates a new contact and merges them together.
How do you make it so that the form submission updates the already existing contact instead of creating a new one and merging the two together?