router.get('/spotifyLogin', (req,res) => {
    const state = generateRandomString(16);
    const scope = 'user-read-recently-played';
    const queryParams = querystring.stringify({
        response_type: 'code',
        client_id: client_id,
        scope: scope,
        redirect_uri: redirect_uri,
        state: state
      });
    
    res.redirect(`https://accounts.spotify.com/authorize?${queryParams}`);
});

router.get('/callback', (req,res) => {

    
    const authorizationCode = req.query.code || null;
    const state = req.query.state || null;

    axios({
        method: 'post',
        url: 'https://accounts.spotify.com/api/token',
        data: querystring.stringify({
          grant_type: 'authorization_code',
          code: authorizationCode,
          redirect_uri: redirect_uri,
        }),
        headers: {
          'content-type': 'application/x-www-form-urlencoded',
          Authorization: `Basic ${new Buffer.from(`${client_id}:${client_secret}`).toString('base64')}`,
        },
      })
        .then(response => {
          if (response.status === 200) {
            res.send(response.data)
        
          } else {
            res.send(response);
          }
        })
        .catch(error => {
          res.send(error);
        });
});

我正在定制express api服务器https://developer.spotify.com/documentation/general/guides/authorization/code-flow/上执行spotify授权代码流。
当我向令牌url发出post请求时，我应该在www.example.com中得到一个json对象response.data，但是我得到了奇怪的字符Screenshot of response.data