So long story short as we can't use RingOut as a super admin with another users extensionID per this topic I downloaded the Javascript SDK and basically used the demos that were provided.
This works fine in Chrome but I have end users using Internet Explorer (and can not use Chrome for various reasons) and what we're seeing is users are getting a blank page after logging in to RingCentral and authorizing our app.
The blank page is our return page i.e. demo/oauth/redirect.html
F12 browser developer tools shows error "RingCentral" is undefined. Are there issues with this SDK and Internet Explorer 11?