Forbiideen Error

const express = require("express");
const mongoose = require("mongoose");
const bodyParser = require("body-parser");
const cors = require("cors");
const axios = require("axios");

const app = express();
const PORT = 3001;

app.use(cors());
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));

const UPSTOX_CLIENT_ID = "ID"
const UPSTOX_CLIENT_SECRET = "c-secret";
const UPSTOX_REDIRECT_URI = "https://api.upstox.com";
const UPSTOX_API_VERSION = "v2";

mongoose
  .connect(
    "mongodb+srv://vsmarttrading97:<password>.mongodb.net/Node-APi?retryWrites=true&w=majority"
  )
  .then(() => {
    console.log("Connected to MongoDB");
  })
  .catch((err) => {
    console.log("Error connecting to MongoDB:", err);
  });

// Upstox login endpoint
app.get("/upstox-login", async (req, res) => {
  const authorizeUrl = "https://api.upstox.com/v2/login/authorization/dialog";
  const queryParams = {
    client_id: UPSTOX_CLIENT_ID,
    redirect_uri: UPSTOX_REDIRECT_URI,
    apiVersion: UPSTOX_API_VERSION,
    state: "your_state", // Optional
    scope: "your_scope", // Optional
  };
  const upstoxLoginUrl = `${authorizeUrl}?${new URLSearchParams(queryParams)}`;
  res.json({ loginUrl: upstoxLoginUrl });
});

app.get("/upstox-callback", async (req, res) => {
  const code = req.query.code;
  console.log("Received authorization code:", code);

  // Exchange code for access token
  const tokenUrl = "https://api.upstox.com/v2/login/authorization/token";
  const tokenParams = {
    code: code,
    client_id: UPSTOX_CLIENT_ID,
    client_secret: UPSTOX_CLIENT_SECRET,
    redirect_uri: UPSTOX_REDIRECT_URI,
    grant_type: "authorization_code",
  };

  try {
    const tokenResponse = await axios.post(tokenUrl, null, {
      headers: {
        "Api-Version": UPSTOX_API_VERSION,
        "Content-Type": "application/x-www-form-urlencoded",
        Accept: "application/json",
      },
      params: tokenParams,
    });

    const userData = tokenResponse.data;

    // Store user data in MongoDB
    const newUser = new User(userData);
    await newUser.save();

    // Send a response back to the frontend
    res.json(userData);
  } catch (error) {
    console.error("Error exchanging code for token:", error.message);
    res.status(500).json({ error: "Internal Server Error" });
  }
});

app.listen(PORT, () => {
  console.log(`Server is running on http://localhost:${PORT}`);
});



I believe this is the same discussion as mentioned previously.

yes its the same discussion as mentioned prev.
here i am sending backend, frontend code




above all backend code.
below frontend code.

i am following the given documents, why i am getting errors and rendering to Swagger UI.
please guide me