Hi @Sarah Bowden4,
With landing pages you can upload a file but not guaranteed that MP3 will work .
You have an option to upload a file and Video. You can check this:
How to Add Images and Video to Forms & Landing Pages3
For the video option, you can upload your MP3 to YouTube, once done get the URL of that page and upload it to your Camden landing page.
I hope it helps. If you're still having issues you can always reach out to firstname.lastname@example.org.