Hi there,

I am sorry for the late reply for this. It seems like your og:image is only 795 x 160px and Facebook minimum requirement is 600 x 315px (Please refer this link: https://developers.facebook.com/docs/sharing/best-practices#images ). Can you try to change to a larger image and see how it goes?
Please refer this screenshot: http://screencast.com/t/WTehLlXvS4pG
Kindly get back to us if the issue still persist on your site and we will assist you accordingly.

I have changed the size to 600 x 315 and it still doesn't show up?

Looks like there is some issue with your site when you turn on gzip compressions. Facebook wasn't able to read the contents on the site.

There is a plugin that solves this issue as this problem is actually from Facebook itself. http://extensions.joomla.org/extension/facebookfix