I am having the same issue. I downloaded Mojave from the app store and it too gave me the 22MB installer file. I was doing some research and found that was normal, and basically grabs the rest during the install. Im having the worst time just trying to upgrade to a SSD with a fresh install of MacOS. Ive deleted the install file and redownloaded from the app store and I get the same file. It downloaded that file fine, but during the install process, after choosing which hard drive i want to install on, I received this error approximately halfway through what was going to be a 5 hr install. I've booted and done this in safe mode and this is the furthest ive gotten.
I've just followed the link posted above by Buscar. That link gave me a link to the app store. After deleting the file again, I downloaded it again from this path and I got the same result, 22.8MB file. I am attempting the install again.