Hi Didey,
Based on your screenshot it seems that you are using Advanced Custom Fields (ACF) plugin for featured images.
Plugin "Sync Posts Between Sites" does not support ACF image data. Only textual fields made with ACF are supported.
This is also stated on the plugin's page under FAQ section and you can find more details there.
You may try a work around to sync only url of the image that you will add in the new textual custom field and load that url as image source in the image html tag on the receiving site.
Syncing of the ACF image data sounds interesting and we may consider adding support for it in one of the future plugin versions.
Hope this info helps.
Happy Syncing!