Deployment on heroku crashing - heroku

Question

I am deploying my MERN application to Heroku. The build is successful but when I open my application the web page shows application error. I checked logs but couldn't understand much from that.
This is my first deployment of an MERN application, so please guide me. Thankyou.
These are the logs
server.js
const express = require('express');
const connectDB = require('./config/database');
const path = require('path');
const app = express();
const PORT = process.env.PORT || 5000;
// Connect Database
connectDB();
// Init Middleware
app.use(express.json({extended: false}));
// Defining Routes
app.use('/api/users', require('./routes/users'));
app.use('/api/contacts', require('./routes/contacts'));
app.use('/api/auth', require('./routes/auth'));
// Serve static assets in production
if(process.env.NODE_ENV === 'production') {
// Set static folder
app.use(express.static('client/build'));
app.get('*', (req, res) => {
res.sendFile(path.resolve(__dirname, 'client', 'build', 'index.html'));
})
}
app.listen(PORT, () => {
console.log(`Server started on port ${PORT}`);
});
server's package.json
{
"name": "contact-keeper",
"version": "1.0.0",
"description": "Contact Manager App",
"main": "server.js",
"scripts": {
"start": "node server.js",
"server": "nodemon server.js",
"client": "npm start --prefix client",
"clientinstall": "npm install --prefix client",
"dev": "concurrently \"npm run server\" \"npm run client\"",
"test": "echo \"Error: no test specified\" && exit 1",
"heroku-postbuild": "NPM_CONFIG_PRODUCTION=false npm install --prefix client && npm run build --prefix client"
},
"engines": {
"node": "12.18.3"
},
"keywords": [],
"author": "",
"license": "ISC",
"dependencies": {
"bcrypt": "^5.0.1",
"config": "^3.3.6",
"express": "^4.17.1",
"express-validator": "^6.12.1",
"jsonwebtoken": "^8.5.1",
"mongoose": "^5.13.4"
},
"devDependencies": {
"concurrently": "^6.2.0",
"nodemon": "^2.0.12"
}
}