Alternatively to surveys, adding URL parameters in the src of the form iframes is not working.

For example:

<iframe src="https://app.mywebsite.com/widget/survey/UOOxm5PTq?partner=MyPartner&ref=JohnSmith" ...></iframe>

This would prefill the hidden fields "partner" with "MyPartner" and "ref" with "JohnSmith" for surveys, but does not work for forms.

This is an amazing feature for surveys, as I can make a single survey for multiple partners and attach the appropriate tracking parameters I need. For forms, I would need to create a form for every single partner so I could add the data I need to pull and I would also be unable to add any data dynamically.