Using the HTML editor, you are able to add the source code of your form or any page into the player as an Event. This could be pre, mid or post-roll.
When you reach the Event in the player, it shows a blank form - apart from any content that was placed directly inside the Event.
This is called a "Mixed Content" error. This is when you are on a secure site (one that starts https://) but the iframe is being delivered insecurely (starting http://). You can determine that if you check the browser console and see this message:
Ensure that both pages are delivered securely over https. To accomplish this, you may need to purchase and install an SSL certificate through a trusted Certificate Authority.