云函数axios请求stringify response to json failed？

router.get('/wyu/jwxc/login', (req, res) => {
  try {
    (async () => {
      let img = await login()
      res.send({
       data: "data:image/jpeg;base64," + img
      });
    })()
  } catch (error) {
    res.send({
      img: 500
    });
  }

})

不知道为什么会报错？