iframe not working any more showing blank page

I am using iframe plugin to display a page which has a finance form for our company, it is a working page meaning that it can be filled out and submitted. When I first installed the plugin everything worked perfectly now the iframe plugin will not display the page I was using. I tried all the fixed I could find in this plugin support forum and none of them worked. All I get is a blank page, I would appreciate any help I can get with this.

https://www.ads-software.com/plugins/iframe/