How to use send_resp?

Hi I have endpoint
/upload/slide-image for uploading image to amazon s3.

After complete uploading I need to send response to client which is Reactjs.

def upload(conn, params) do
  # uploading code 
  #send response to the client with amazon s3 image url
  send_resp(conn, 200, image_url)

I am calling this controller in client side using fetch api

fetch(server_url, { method: "POST", body: data })
.then( response => console.log("Printing response: ", response);

but Response object in client is empty.

Response {
  body: null
  bodyUsed: false
  headers: Headers {}
  ok: false
  redirected: false
  status: 0
  statusText: ""
  type: "opaque"
  url: ""

And In browser network tab, I can find image url in response tab, So my server sending response. But How can I send_resp for Response object in client side?

Have you verified image_url is not nil?

Yes it is not nil.