Construction mode background disappears

I am having a tough time getting the background to work. I did get it to work 1 time with a URL, and then it disappeared and gives me a gray background.

I have since made a plain white JPG for the background, and it still shows the plain grey background.

Any ideas?

My site is http://www.globaldimension.com

If I can get this to work, I might splurge for the Pro version, as this is very handy utility.

https://ww.wp.xz.cn/plugins/wp-construction-mode/