Error : Missing or invalid image file

I realized it always chose the wrong image. I had to manually select the other image for each post. Also the facebook posting is lacking functionality and doesnt show the summary card of posts, with the large image, like other similar plugins do.

The answer is here https://www.nextscripts.com/snap-features/how-snap-sets-images/

and here: https://www.nextscripts.com/facebook-posts-with-attached-link/

and here: https://www.nextscripts.com/snap-features/facebook-post-types/

Tried all possible settings you gave the link for. Still didnt work. There is some bug with the functionality. I switched to another plugin (jetpack publicize) and it worked perfectly without any setting configurations. It selected the featured image correctly and showed a large image with link and description perfectly.