How to correctly attach the goal to submit the form if the form is loaded by an iframe - ohm?

Question

Yandex.Metrica

There is a small landing page with a questionnaire, the
questionnaire is loaded by iframe using Fancybox3.
iframe form.
How to properly attach a target to submit a form?

Answer 1

Make a "Thank you" page if the fencibox allows. You can also set a goal through JS, look for ready-made scripts, or maybe someone else here will tell you.