Access denied while uploading IFrame in IE11

I'm inserting an own iframe created by me on my page, specifically it's a chat bubble, and for both Chrome and Firefox as IE Edge works correctly, but for IE11, it does not return access denied.

What I do on my main page is call a JS in which I create an Iframe, and once created inside the event window.load I call a function of that Iframe to load the chat, but that's when I gives the access error.

Iframe created it this way, I do not know if it can be done differently than inserting the HTML instead of pointing to a URL

//Creamos Iframe para almacenar todo el chat
var iframe = document.createElement('iframe');
//propiedades iframe
iframe.setAttribute('id', 'contentChat');
iframe.setAttribute('name', 'chatBot');
iframe.setAttribute('scrolling', 'no');
iframe.setAttribute('allowfullscreen', '');
iframe.style.cssText = 'border:none;';
iframe.setAttribute('src', 'https://prepro.de/client/html/webIframe.html'); 

* The route is modified to maintain the privacy of the site to be a company

When I call the Iframe function to start the chat, I get that error

var el = document.getElementById('contentChat');
        var iframeDoc = getIframeWindow(el)

        iframeDoc.initializeChat(params);