No preview when using dropbox add-on

Hi,

I’ve downloaded and installed the plugin and add-on for dropbox as well.
Works great, but i’m not getting any preview image of the file.

They are JPG files, so a preview is crucial as the client can then see which image he/she needs to download.

We want to use this as a clientportal so users can login and download promotion materials to use on their own social media/website.

How can I fix this?
I prefer not to use the featured image option in wordpress, as our files are on dropbox, so that would mean we need to make custom thumbnails and upload them as well.

Many Thanks,

Regards,
Mirna