Here are two possible casues to the problem and the solutions:
1. The site is hosted on WordPress.com
WordPress.com is different from WordPress.org self-hosted sites configuration, for example, the files and folders structure. And our plugin is developed based on the WordPress.org platform and currently does not(yet) support WordPress.com.
2. The site is on a Nginx server
If your web server is Nginx, please follow this guide to add specific rules to Nginx conf. file to make the staging site to work properly.
3. Cache, redirect or security plugins settings
It is recommended to temporarily deactivate(once the staging site is created, you can re-activate them) all cache, redirect and security plugins on the live site to rule out possible problems.