Not sure what kind of iTunes music files you have collected. As far as I know, if they are downloaded from iTunes Apple Music Store, they could probably be protected with DRM. That's to say, in this case, you won't be able to sync your iTunes music to Poweramp Android as DRM-ed iTunes music files can only be supported and played by Apple's devices. In this way, you must use some special tools like TunesKit Apple Music Converter, Aimersoft, Requiem, etc. to get rid of the DRM from Apple Music for good.