Thumbnail previews are automatically generated when you type/paste a link in the compose screen. This reflects how your audience would view your post if you share the same link natively from the social channel.
- Facebook: On Dec 18, 2017 Facebook removed the ability to customize link attachments. That means, a thumbnail will be automatically set for the link, which you cannot edit.
To customize the thumbnail image of the links before you publish them to your Facebook page, you'll first have to verify your domain on Facebook.
- Twitter: Due to Twitter's API restrictions, we can't show thumbnail previews for Twitter in the Publishing window. However, your published post will have a thumbnail preview automatically generated from the link.
- LinkedIn: When the link you add to the Publishing window has multiple images, you can navigate and select a different thumbnail image by clicking the arrows.