Hi Olga thanks for the reply.
This error is repeated on both sites every time I try to install the plugin.
Installing plugin from uploaded file: XStore_Theme_v.8.1.5.zip
Unpacking the package…
Installing the plugin..
The package could not be installed. No valid plugins were found.
Plugin installation failed.
Go to Plugin Installer
One standard license is valid only for 1 project. Running multiple projects on a single license is a copyright violation.