If you like to create a clone of a WordPress staging site which you’ve created earlier with WP Staging you need to do a slight modification in the database, first.
Open up one of your favorite database administration tool like phpmyadmin or the one-file solution adminer.
Look for the entry
wpstg_is_staging_site in the table
option_value to false or remove that entry at all.
After doing that you are able to clone the staging site as usual by going to your Staging site > WP Staging > Sites
What does this value do?
This setting is responsible for telling WP Staging if the current site is a staging site or not. So, set this value to false if you want to clone the staging site. WP Staging will treat the staging site as a production site then which allows you to create another clone of it.