Change background for mobile

I successfully used the given options here (mobile background generate blocks | WordPress.org) to change backgrounds for mobile. Now I am trying this for another web site (test – The Interior Retreat Langweer), but I can’t get it working. Would it be possible for you to take a look? I only want to change the background of the last block for mobile… I am using the free version of this great plugin.

Thank you!
Eva