I recently upgraded from 1.4.1 to 2.1.1.
My previously working embedded forms no longer worked. I was getting a 403 error.
Looking in the browser console, I noticed that they were being redirected as a POST to a GET using a 301 redirect. Since a GET is not allowed for the form submission, it resulted in a 403.
I looked at the cut-and-paste code recommended in Mautic for the form, and it included:
Since none of my other pages use the "/index.php" portion in the URL, I changed it to:
<form autocomplete="false" role="form" method="post" action="https://myhost.com/form/submit?formId=8"
Now the form is working again.
I created a new form after the upgrade, and the URL does not contain the "/index.php" portion. I guess the cut-and-paste code must get saved somewhere with the form configuration from the previous version of Mautic, so it still shows the previous version of the URL.