The initial download is 1.3gb. Need this minimum just to download the apk.
Then you need 5-6 GB as it UNPACKS the APK installer package. This is where it fails usually. Due to not enough storage space to write the temp cache for the installer package + run the installer, AND write the new data to your mobile devices micro-sdcard, or hdd/ssd.
That said Majalis Duo should add this to their stores description.
That said. Hope this helps address the issue. No I am not affiliated with Majalis Duo other than a fan of the game.