The particular option should be enabled to apply featured image. See the picture below.
Featured image can be specified only by add extended attribute in the document named ‘featured_image’ or ‘Featured Image’.
The attribute’s value can be:
- The URL of existing WordPress media picture (marked as link or not) or inserted linked image with that URL. The plugin detects that picture URL is the media picture and set it as featured image.
- Embedded or linked image as similar as body image. In this case the image will be automatically uploaded and set as featured image.
Note: Image is always placed in the media library.