:( it doesn't work 
It does work.
The package appears to be invalid, not because there could be something wrong with your device, It's because the package has the same name as another gacha club mod/app installed on your device, which makes your device think that the package Is invalid, you will not be able to install Gacha Art If you do not uninstall the other Gacha Club apps installed on your device.
However, you can install Gacha Art without having to uninstall other apps If you change the name of It's package with an apk editor/manager, you can find said apps by searching for them on google, the ones I use are apk editor master and apktool M, both are good and always solve this issue(app not installed as package appears to be invalid).
If you don't know how to use the apk editor and couldn't find a tutorial that properly shows/explains how to rename an app's package, I can send a video tutorial that I recorded.
I am not sure If this will work for everyone, If renaming the package with an apk editor doesn't solve the issue, you will need to uninstall Gacha Club and a Gacha Club mod to install Gacha Art, or you can give up on trying to install it.