When you share a URL on Facebook, Facebook downloads and caches meta data about that page. This meta data includes items like meta description, title, and a thumbnail image. Facebook uses this information to describe the link or URL when it is posted and shared on Facebook.
Unfortunately, Facebook doesn't always refresh or update their cache each time a link is shared. If you've made changes to your site's meta data and want to see that reflected on Facebook, you'll need to use Facebook's developer tools to do so.
1. Open the Open Graph Object Debugger
2. Enter your URL and click the "Show existing scrape information" button
3. Verify the data is correct. If it isn't, click the "Fetch new scrape information" button
Facebook Open Graph Object Debugger
Facebook Developer Tools