I am another staff checking in and I have logged in to your site successfully. I found out that as what Nabeel has mentioned, your site URL and WordPress address URL is different from your WordPress dashboard url.
If your staging site resides in a different folder, you must force the urls to be the same as your WordPress dashboard URL. To do that, you will need to edit your wp-config.php file of your staging site and add this:
example.com should be the name of your domain of course. You will have to do this because Pro editor will use the URL settings to load the preview.
Hope this helps.