This was the error message:
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Playback failed
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Fiddler has encountered an unexpected problem. If you believe this is a bug in Fiddler, please copy this message by hitting CTRL+C, and submit a bug report at http://www.telerik.com/forums/fiddler.
Sound API only supports playing PCM wave files.
Type: System.InvalidOperationException
Source: System
at System.Media.SoundPlayer.ValidateSoundData(Byte[] data)
at System.Media.SoundPlayer.LoadAndPlay(Int32 flags)
at Standard.ResponseWebView.btnPlay_Click(Object sender, EventArgs e)
Fiddler v5.0.20173.50948 (x64 AMD64) [.NET 4.0.30319.42000 on Microsoft Windows NT 10.0.16299.0]
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OK
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Granted the error message does give helpful stuff like: "Sound API only supports playing PCM wave files."
Which means the response was likely just incorrectly assumed to be a wave file.
I clicked the PLay button on the WebView becuase none of the other views are useful.
I would really just like to download a version of the file and then play it from another application but I do not know how in Fiddler and that would be the larger issue.