If you are using WordPress and the All in One SEO plugin, go to Social Meta and select: Use AIOSEO Title and Description; and enter your OG image source. Verify your settings by viewing the page source in your browser, for example:
Go to the Facebook sharing debugger https://developers.facebook.com/tools/debug/sharing/
Enter your website URL and click debug. You should see something like this, with no errors reported. If not scrape again, and again a few times, as there is a cache involved here that has to be forced.
You can do a final check in Facebook by typing in your website address into a post then hit the space bar on your keyboard (NOT ENTER). Remember to insert a single space after your URL.
A preview should appear and if everything worked, it should look exactly like the Link Preview on the Sharing Debugger page.