Issue in path of deployed MERN app on heroku - heroku

Question

getting Error: ENOENT: no such file or directory, stat '/app/client/build/index.html'
package.json
"name": "google-contacts-backend",
"version": "1.0.0",
"private": true,
"scripts": {
"start": "node ./bin/www",
"dev": "nodemon ./bin/www",
"test": "nyc _mocha --timeout 10000 --exit --report lcovonly -- -R spec",
"lint": "eslint --fix --config .eslintrc.json \"**/*.js\"",
"heroku-postbuild": "cd client && npm install --only=dev && npm install && npm run build"
},
"dependencies": {
"axios": "^0.19.2",
"bcrypt": "^3.0.6",
"codacy-coverage": "^3.4.0",
"cookie-parser": "~1.4.3",
"cors": "^2.8.5",
"debug": "~2.6.9",
"dotenv": "^8.2.0",
"express": "~4.16.0",
"express-jwt": "^5.3.1",
"express-validator": "^6.2.0",
"googleapis": "^58.0.0",
"jsonwebtoken": "^8.5.1",
"mocha-lcov-reporter": "^1.3.0",
"moment": "^2.24.0",
"morgan": "~1.9.0",
"nodemailer": "^6.3.1"
},
"devDependencies": {
"chai": "^4.2.0",
"chai-http": "^4.3.0",
"eslint": "^6.5.1",
"mocha": "^6.2.2",
"nodemon": "^1.19.4",
"nyc": "^14.1.1"
}
}```
server.js
```app.get("*", (req, res) => {
res.sendFile(path.join(__dirname, "client", "build", "index.html"));
});
when I tried to check client folder directly in heroku bach, it was empty.