Are you putting the form on an LP that is itself in an IFRAME?
You know, I am not quite sure, I just pick one of the custom template.
I'm guessing that has to do with the parameter acting weird?
If you had an LP inside an LP then you would be forced to use the referrer. Normally this would not work, nor be necessary.
Ah I see, I will keep this in mind.
Because we won't use this landing page later on.
I worked on a similar project recently and these two pages helped me:
For the email: https://www.checkmarket.com/kb/embed-the-nps-question-in-the-survey-email-invitation/
For the landing page: https://jennamolby.com/how-to-display-dynamic-content-on-a-page-using-url-parameters/
The links are aren't really relevant (more like wrong!) for Marketo forms and LPs.