If Facebook doesn't seem to be posting the most recent text and image you added to the Social Media section, you likely need to run a Facebook refresh.
First, make sure your Social Media settings are what you'd like to share to Facebook.
Save and publish your changes if needed. Then copy your page's live URL.
Copy the URL into the Facebook debugger below.
Enter your page's URL, then click the Debug button.
Click 'Scrape Again'.
Now when you share to Facebook, the updated details will post.
Note: If the image isn't showing up at all, check to see if the image file name has any spaces or special characters in it. That can sometimes result in a blank image. A solution would be renaming the file with no spaces or special characters, re-upload the image in the RegFox's Social Media editor, then Republish the page. After the image update, re-scrape again using Facebook's Sharing Debugger.
What about my LinkedIn post?
You will find a similar tool to accomplish this here: https://www.linkedin.com/post-inspector/