Sound not playing on Galaxy S4 device

I'm making a small language vocab card game in which I'm using a HTTP Get/Post to a Text to Speech API in order to get the proper pronunciation of a vocab word. Everything works fine in the inspector, but when I tried it on my Galaxy S4 device, it did not work.

Some details on the sound clip: it's in MP3 format and 48kHz 16bit stereo. Here's some code:

 IEnumerator waitForRequest(WWW www) {
     
     yield return www;
 
     if (www.error == null) {

         AudioClip audio = www.GetAudioClip(false, false, AudioType.MPEG);

         StartCoroutine(playClip(audio));

     } else {
     
         Debug.Log("there's an error.");
         Debug.Log(www.error);
     }
 }

 IEnumerator playClip(AudioClip audio) {
 
     source.clip = audio;
     source.Play();
     isVoice = true;
     yield return new WaitForSeconds(audio.length);
     isVoice = false;
     source.Stop();

 }

AudioSource and AudioListener are attached to the main camera. I'm using it from code attached to another GameObject. The sound files I'm getting back are really short.