Can't Put.mp3 files onto my iPhone 4S via iTunes?

MacBook Air, latest version of OS X, iTunes, and iOS… But my Mac won't let me put.mp3 files onto my iPhone… Why is this?

.mp3 is an older format i have iConverter downloaded to my computer (MAC) and it works well for converting a file from.mp3 to.mp4 in just a couple seconds and then its easy to just sync after i have added them to my iTunes library

  • Transferring MP3 to iTunes, MP3 not working? I downloaded 40 MP3s in my computer and as usual, I drag them to iTunes so I can connect it to my iPhone. But only 4 were able to transfer. I tried playing the MP3s that didn't work in windows media player but they did not play. They are all MP3 files (the ones that worked and didn't work) how can I make the files play and transfer them to iTunes?
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