Okta-auth-js compatibility issue with IE11

Implemented Okta with pkce flow. We have older version of angularjs(1.4) and integrated our application with okta-auth-js. It is working fine in chrome but trying to make it work in IE. I am following the documentation from here https://github.com/okta/okta-auth-js to make it work in IE but when I tried to add okta-auth-js.polyfill.js file in a <script> tag, it is failing to load polyfill.js resource.

Any help is much appreciated.