Error when trying to install 3rd party apps

[AC Question]

I have 3rd party apps enabled but when I try to install the app from the apk download file I get an error saying "Unable to scan filename.apk".

I'm on Android 6.0, don't know if this means the apk apps are not compatible anymore.

 

[Rukbat]

It probably means that the file is corrupt. Put it on a PC, change the filetype to zip (an apk file is really a zip file) and test it with a zip program.