Javascript embed referer is blank?

I am trying to get comments to embed on my site - in the iframe source I see:

<div class='embed-error'>
      <p>Referer:<code></code></p>
      <p>The referer did not match any of the following hosts:</p>

Can anyone tell me where it gets Referer from?

Based on other posts it should say

Referer: the-url-that-referred || and not be blank

It’s not matching my embed host because it is blank so it doesn’t matter what I have in the embed hosts.

Any help would be greatly appreciated!