Facebook eliminated the feature and the ability to customize link previews for Facebook group and profile posts.

As of July 17 at 11:59 pm PST, Facebook eliminated the feature and the ability to customize link previews for Facebook group and profile posts, in an effort to reduce misrepresentation of link content.
These changes will apply to all of Facebook’s API integration partners.
It will no longer be possible to customize the image, title or description of a link preview in Facebook profile or group posts. Pages will not be affected by this change until a later date.
Facebook pulls link previews from website metadata. If you share a link to a website that is not your own, be aware that it may not have this metadata available. So a complete link preview with an image may not be generated in some cases.
A very critical change for business bloggers and website pages. Be very precise when adding web pages to your website that the page has an appropriate title. If you are blogging make sure your blog has an appropriate title and carefully select images.
Facebook will pull from the Metadata. Make sure if your blog or site has a place to add metadata that you carefully select and ad this information so that it will preview correctly.
Here is a tip: You can go to the Open Graph Debugger and put in your link. This tool will let you see exactly what your post will look like in Facebook. Youhave the ability to fix a few things. https://developers.facebook.com/tools/debug/og/object
Notice from Facebook: “By removing the ability to customize link metadata (i.e. headline, description, image) from all link sharing entry points on Facebook, we are eliminating a channel that has been abused to post false news.”
Here are the news briefs from Facebook developers:
https://www.facebook.com/business/help/247886969033572
https://developers.facebook.com/blog/post/2017/06/27/API-Change-Log-Modifying-Link-Previews/
https://developers.facebook.com/blog/post/2017/06/27/API-Change-Log-Modifying-Link-Previews/