I have resolved the issue. There was an error somewhere in my .htaccess file which prevented access to my images. I reset it to the default and now everything is working fine!!
I did try setting the image using Yoast SEO, but it didn’t have an effect. Also, I did install an Open Graph plugin to try to fix the issue but again no luck. I continue to get a grey image when I try to share to Facebook or twitter.
Thank you,
Sofia