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

Why this happens

This error appears when you try to upload a theme file in the Plugins section. WordPress checks for a valid plugin file and fails when the upload is actually a theme.

How to fix it

1. Make sure you’re uploading a plugin file, not a theme.
   • Plugin files are installed under Plugins → Add New.
   • Theme files are installed under Appearance → Themes → Add New.

Tip

If you meant to install a theme, upload it through Appearance → Themes → Add New instead.