One thought that comes to mind is that maybe you need to set the "Allow installation of apps from unknown sources" under settings/security. This will block installation of anything that didn't come from the Google play store.
If that doesn't help, you might want to look at a logcat log from the time when you are trying to install the app through appgallery. That might give a clue to what the issue is.
Unknown sources had already been selected for when I moved the .apk over manually via usb and installed it that way.
Though I did manage to solve it. I needed to use the signed version of the app.