Some of my music was purchased on iTunes, some on Amazon, some “fell off a truck.” I’m trying to find a music player that will play them all without caring where the file came from. I had found a workaround by putting files in my Dropbox, then making them available when offline, and playing them using an app called Jukebox—an app that’s no longer available.
The main times I want to listen to music is when I have no phone service, so any “cloud” solution is pretty pointless. In addition, I can’t use iTunes because of an “invalid response was received from the device” issue.
If you purchased this music in the past 9 years or so, the built-in Music app on your iPhone shouldn’t care where they came from and will play them. That includes your off the truck music, provided the files are in a common format like mp3 or m4a.
The invalid response message usually means there is a USB problem. Try a different USB port on your computer (don’t connect via a USB hub) or try another cable. If you can still see your phone in iTunes when you connect via USB (even if you can’t transfer songs to it because of the invalid response message), try enabling “Sync with this iPhone over Wi-Fi” and “Manually manage music and videos.” That way you won’t need USB for any transferring.
At the very least, you should be able to re download your purchased iTunes music directly to your iPhone. In the iTunes Store app, tap the More button, then Purchased > Music > All Songs and tap the iCloud button next to the songs you want to download or tap Download All at the top right.
I purchase all my music on Amazon and then download it. Then I import it into iTunes and sync it with my phone. The downloaded music goes from my computer to my phone via iTunes.