Question DownloadHandlerAudioClip audioClip's loadState is Unloaded

unity version:2020.3.1f1
os:windows 10

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Networking;

public class Test : MonoBehaviour
{
// Start is called before the first frame update
void Start()
{
var url = "file:///c://biu.mp3";
DownloadHandlerAudioClip dlh = new DownloadHandlerAudioClip(url, AudioType.UNKNOWN);

UnityWebRequest request = new UnityWebRequest(url, "GET", dlh, null);
request.SendWebRequest();

dlh.compressed = true;
var audio = dlh.audioClip;
Debug.Log(audio.loadState);
}
}

the audio's state is Unloaded. the error is:

Error: Cannot create FMOD::Sound instance for clip "" (FMOD error: An invalid parameter was passed to this function. )
UnityEngine.StackTraceUtility:ExtractStackTrace ()

can some body help me??? i am not familier with audio.

the audio mp3 file is below.

i just changed the file format to .txt. when run, please change to .mp3. Thank you!!