If you're getting the error 803-3009 (which is common), just download Root Explorer APK, go to data/data, find nintendo.zaba or so and delete the shared pref folder.
Hey Sakimii, you can download the QooApp apk file online, install QooAPP and use that app to download FEH on NOX
Not sure if you're trying to mod FEH or use summon injections but I think they've changed since the update 2 days ago.