My guess is you do not have any frames in your animation yet? If you just opened Animation Paper and imported the sound, your animation is only 1 frame long. Try dragging down on the one frame in the X-Sheet to make a larger number of clones – then you have something to play, including the audio. Also you should now be able to see your audio as a waveform.
Let me know if that helped you – or if your problem is something else?