mongoose.connect(), URI parameter must be 'string', got 'undefined'. db.js and server.js issue

I am receiving this error message:

MongooseError: The `uri` parameter to `openUri()` must be a string, got "undefined". Make sure the first parameter to `mongoose.connect()` or `mongoose.createConnection()` is a string.

This is my project structure

ROOT
|_ node_modules/
|_ package.json
|_ yarn.lock
|_ client/
|_ database/
|   |_ node_modules/
|   |_ db.js
|   |_ package.js
|   |_ .env
|   |_ yarn.lock
|_ server
    |_ controllers/
    |_ middleware/
    |_ routes/
    |_ server.js
    |_ package.json
    |_ yarn.lock 

I am able to connect to database if I call the database function inside db.js file like so:

require('dotenv').config()
const mongoose = require('mongoose')

// Database connection
const URI = process.env.ATLAS_URI
console.log(URI)

const mongoDB = async () => {
    try {
        // Passing additional connection parameters for connect()
        const connectionParams = {
            useNewUrlParser: true,
            useUnifiedTopology: true
        }
        
        // Connect to database
        await mongoose.connect(URI, connectionParams)

        // Log when connected to the database
        console.log('Connected to database ✅')

    } catch (error) {
        console.error('Error connecting to Database ❎\n', error)
    }
}

mongoDB()

However I use module.exports = mongoDB as a function to my server.js I encounter error. Here is the script for my server.js file

const express = require('express')
const mongoDB = require('../database/db')
const app = express()
const port = 1234

// Try to connect to the database
mongoDB()

// Start listening to the given port
app.listen(port, () => {
    console.log(`Server running on port ${port}`)
})

I have also checked my .env file and everything looks good also I have tested my connection string whether it is being read properly by logging the URI in the db.js file. I am able to see the connection string from the log. If anyone who has faced the similar issue. Please guide me through the process to fix this issue.

ok try give you dotenv package path option maybe it's fix your poblam

require("dotenv").config({path:"your dotenv file path"})