why is my mern app deployed on heroku using local server

Question

I deployed my MERN app on heroku it is working fine. However, the deployed app uses my local server. when I stop my local server, the deployed app stops working. What am I doing wrongly?

Here is my package.json file
{
  "name": "careplan",
  "version": "1.0.0",
  "description": "careApp",
  "main": "app.js",
  "scripts": {
    "start": "node server.js",
    "start:prod": "SET NODE_ENV=production&& server.js",
    "debug": "ndb server.js",
    "dev":"nodemon server.js",
    "heroku-postbuild": "cd client && npm install --only=dev && npm install && npm run build"

  },
  "engines": {
    "node": "16.13.1"
  },
  "author": "Oladimeji Shopeyin",
  "license": "ISC",
  "dependencies": {
    "bcrypt": "^5.0.1",
    "cors": "^2.8.5",
    "dotenv": "^14.2.0",
    "express": "^4.17.2",
    "jsonwebtoken": "^8.5.1",
    "mongoose": "^5.13.14",
    "morgan": "^1.10.0",
    "validator": "^13.7.0"
  },
  "devDependencies": {
    "eslint": "^8.7.0",
    "eslint-config-airbnb": "^19.0.4",
    "eslint-config-prettier": "^8.3.0",
    "eslint-plugin-import": "^2.25.4",
    "eslint-plugin-jsx-a11y": "^6.5.1",
    "eslint-plugin-node": "^11.1.0",
    "eslint-plugin-prettier": "^4.0.0",
    "eslint-plugin-react": "^7.28.0",
    "nodemon": "^2.0.19",
    "prettier": "^2.5.1"
  }
}