The Audio files in My cloud Home duo are not played by Android phone. Simply it is saying 'not supported file ’
See the dedicated subforum for the My Cloud Home Duo. This subfoum (My Cloud) is generally for the single bay My Cloud device which is different than the My Cloud Home line of devices.
Also see the dedicated subforum for the mobile apps.
Lastly check the My Cloud Home Duo User Manual to ensure your audio/sound/media file is supported by the Home Duo and or supported by the mobile app.