Content not loading

I cannot show you a link since it’s behind a firewall that doesn’t allow me to share with external individuals, however, I have taken the following steps and it is still not working completely.

I created a new page, and a second page that I want to load in a modal on that page. I placed the link on the new page with just the slug of the second page (with no forward slashes, then with forward slashes, then with the root folder for the installation of wordpress followed by a slash and the slug) and all it does is open a blank modal overlay with the close icon up at the top right (so that’s working correctly), but it only has an icon that keeps spinning. No content ever shows up in it.

I tried a page, I tried a post, I tried a custom post type all on the same page with the same results.

In looking at my web developer tools, I am not coming up with any errors.

Any ideas what it might be?