Background image not loading in Facebook browser

Hi,

I am promoting a simple landing page via Facebook ads, but when testing my campaign in Facebook the FB website browser does not display the background image. I have attached an image of this and also what it looks like when I just load it in the normal mobile safari browser.

I have tried changing the size of the image and also saving it locally so I can't figure out what is wrong!!

Has anyone else experienced this and know a way around it?