Unable to download a file from my node js server (my backend and frontend are decoupled)

Question

My nodejs backend is running on localhost:8080 and frontend on localhost:8081 using http-server, I am not able to download file from my server side to client side, I am new to node js so facing some problems with it

What I tried

I created a readstream to my required file on server side and then pipe it to res object , also I set some headers :-

res.setHeader("Content-Type","image/png") // as I am trying to download a 
res.setHeader("Content-Disposition", `inline; filename=${filename}`);

But it still fails

Code:-

code for downloading a file from server side

let filename = "hello.png";
let readStream = fs.createReadStream(path.join(__dirname, "..", chatDoc.chatContent));
res.setHeader("Content-Type", "image/png")
res.setHeader("Content-Disposition", `inline; filename=${filename}`);
readStream.pipe(res);

cors code:-

const cors = require("cors");
app.use(cors({
    origin: "http://localhost:8081",
    credentials: true,
    withCredentials: true
}))

frontend code:-

fetch("http://localhost:8080/downloadNow",{
    method:"POST",
    headers:{
      "Content-Type":"application/json"
    },
    body:JSON.stringify({
      chatId:chatId
    }),
    credentials:"include"
  })
  .then((data) => {
    console.log(data);
  })
  .catch((err) => {
    console.log(err);
  })

Response on frontend:- I got successfully response from server but file isn't downloaded.

please help me out with this