Got this "Error: connect ECONNREFUSED 127.0.0.1:4000" error while giving post request

When I am trying to give post request to "http://localhost:4000/api/v1/product/new" url I am getting this error "Error: connect ECONNREFUSED 127.0.0.1:4000". My json text:

{
    "name": "product",
    "description": "this is a sample product",
    "price": 30000,
    "category": "Laptop",
    "images":{
        "public_id": "sample image",
        "url": "sampleUrl"
    }
}

My server.js:

const app = require("./app");

const dotenv = require("dotenv");
const connectDatabase = require("./config/database");

//config
dotenv.config({ path: "backend/config/config.env" });

//connecting to database
connectDatabase();

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

My controller file productController.js:

const Product = require("../models/productModel");

// Create Product
exports.createproduct = async (req, res, next) => {
  const product = await Product.create(req.body);

  res.status(201).json({
    success: true,
    product,
  });
};

exports.getAllProducts = (req, res) => {
  res.status(200).json({ message: "Route is working fine" });
};

My route file productRoute.js :

const express = require("express");
const {
  getAllProducts,
  createproduct,
} = require("../controllers/productController");

const router = express.Router();

router.route("/products").get(getAllProducts);

router.route("/product/new").post(createproduct);

module.exports = router;

And lastly my model file productModel.js is:

const mongoose = require("mongoose");

const productSchema = new mongoose.Schema({
  name: {
    type: String,
    required: [true, "Please Enter product Name"],
    trim: true,
  },
  description: {
    type: String,
    required: [true, "Please Enter product Description"],
  },
  price: {
    type: Number,
    required: [true, "Please Enter product Price"],
    maxLength: [8, "Price cannot exceed 8 characters"],
  },
  ratings: {
    type: Number,
    default: 0,
  },
  images: [
    {
      public_id: {
        type: String,
        required: true,
      },
      url: {
        type: String,
        required: true,
      },
    },
  ],
  category: {
    type: String,
    required: [true, "Please Enter Product Category"],
  },
  Stock: {
    type: Number,
    required: [true, "Please Enter product Stock"],
    maxLength: [4, "Stock cannot exceed 4 characters"],
    default: 1,
  },
  numOfReviews: {
    type: Number,
    default: 0,
  },
  reviews: [
    {
      name: {
        type: String,
        required: true,
      },
      rating: {
        type: Number,
        required: true,
      },
      comment: {
        type: String,
        required: true,
      },
    },
  ],
  createdAt: {
    type: Date,
    default: Date.now,
  },
});

module.exports = mongoose.model("Product", productSchema);

And my config.env file is:

PORT = 4000

DB_URI = "mongodb://0.0.0.0:27017/Ecommerce"

I also tried, by adding "app.use(bodyParser.urlEncoded({extended:false}))" and cors but still it didn't working.