Iframe video in a CMS page

I’m working on a website with a CMS knowledge base. I want to put an iframe for a video on some of the knowledge base pages. The videos are hosted on Wistia.
I put the embed link on the Knowledge Base template page, put a plain text section onto the CMS that I could put the iframe URL into. I then linked them up but after publishing, it was blank where the video should be.
I found this tutorial for getting an iframe to work for a podcast and assumed that it would roughly be the same idea for adding a video. I got further this time because it was now showing a 400 error.
Could someone please point out to me what I did wrong? Is there something different that I need to be doing? I’ve attached my read-only link below for you to reference. Thanks!

Here is my site Read-Only: [LINK]1
(how to share your site Read-Only link)

Where is the video? What page & section?

The video is on the Knowledge Base template page. The iframe is in a plain text field in the CMS Knowledge Base Collection settings. The actual iframe code is on the Authorized User CMS page