Greg is running into issues with music he has downloaded via SoundCloud. He gets errors now that say "invalid file." Leo says those are MP3s, so the Samsung Galaxy S7 should play them just fine. It could be an issue with how the file is saved by the app. SoundCloud enables you to stream in SoundCloud, but not play it with an MP3 player. That may mean a bad download, or saving to a format that his player doesn't recognize, or it may even be copy protection.
The chatroom says that SoundCloud has DRM and if his subscription has lapsed, it won't allow him to play the files. Chances are, they're just a bad download, though. Greg should get a file manager from the Google Play store and analyze it. If it's zero bytes, then obviously there's nothing to play. That can happen, too.