My embed block iframe code does not work. Any ideas?

I am trying to use an embed block on my Squarespace site to display the following iframe on a page (content from National Public Radio):

<iframe src="http://www.npr.org/player/embed/455912166/456523060" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player"></iframe>

When I test this iframe code in an HTML code tester such as CSG it works fine.

When I attempt to put the code in an embed block using the "embed data" field (not the URL field), the block displays a pixelated sad face page icon.

When I attempt to put the code in a code block instead of an embed block, I get the same result.

I have tried following the instructions in this Squarespace forum post with no luck.

Does anyone have any idea why this iframe code won't work with Squarespace, or ideas on how I could make it work? I am not a developer but have a somewhat technical background.

Thanks in advance! Cheers.

Well, never mind! After more searching I found this post and reply on the forums. Basically the answer is that there was nothing wrong with my iframe code or how I was entering it into an embed block. The problem is just previewing the specific content of that block while logged into my Squarespace site in admin mode.

I'm confused. I'm having the EXACT same problem with a legitimate embed code. Yet it's rejected. I am logged in! Is that different than an "admin mode"??

If you Squarespace website is using a secure connection (ie. https) then you are now unable to embed a url that uses insecure connections (ie, http://....)

Scoll down to Mixed Content on this page: https://support.squarespace.com/hc/en-us/articles/205815898-Squarespace-and-SSL