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
- 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.



