AdmiralRob, I got it to work by using the link on that page. When it brings me to the Instagram page that requests, authorization, you’ll see this in the last part of the URL:
&redirect_uri=https://davidmregister.com/instagram-widget-for-wordpress/&response_type=code
Change the last word from “code” to “token” and hit Enter. From there, click the “Authorize” button. As of today, that’s what I had to do to get it to work.