The package could not be installed. No valid plugins were found

You may get the following message when trying to install a WordPress theme or a plugin.

Unpacking the package…

Installing the plugin…

The package could not be installed. No valid plugins were found.

Plugin install failed.

Most of the time, this happen when you've tried to install a theme as a plugin.

To install a WordPress theme manually, you need to follow those steps :

  1. In your WordPress dashboard, go to Appearance > Themes > Add New.
  2. From there you’ll see an option for “Upload” at the top of the screen. Click the “Browse” button, navigate your computer files and select the .ZIP file for your downloaded extension. For an in-depth documentation about WordPress theme manual installation, read the official WordPress.org documentation.

If you get this error when trying to install a WordPress plugin manually, this means that the plugin is missing a file or is not properly coded. 

More about plugin installation here : https://codex.wordpress.org/Managing_Plugins#Manual_Plugin_Installation