Chronicle theme – homepage image problem

I have recently installed the (Zinmag) Chronicle theme but can’t get the featured news box to work or any thumbs to chow in the item boxes.

Several people have commented in various forums that by creating a custom field in “screen options” and adding the image url, this solves the problem … but it doesn’t, at least not for me!

Can anybody help me get the images displaying correctly?

My test page is at: https://www.synergynews.co.uk/main/

Any help would be greatly appreciated.