MERN app running on local server but fails during deployment on Heroku

Question

I have this mern app i've been trying to deploy on heroku, it builds and gets deployed successfully with no errors in my terminal but when I open app I instead see Application error. When I do heroku logs --tail in my terminal, I get this "npm ERR! Missing script: "start"". Here is my api/package.json file:

  "name": "api",
  "version": "1.0.0",
  "engines": {
    "node": "14.17.5"
  },
  "description": "",
  "main": "index.js",
  "author": "Emanuel",
  "license": "ISC",
  "dependencies": {
    "bcrypt": "^5.0.1",
    "cors": "^2.8.5",
    "dotenv": "^10.0.0",
    "express": "^4.17.2",
    "helmet": "^5.0.1",
    "marked": "^4.0.8",
    "mongoose": "^6.1.4",
    "morgan": "^1.10.0",
    "multer": "^1.4.4",
    "nodemon": "^2.0.15",
    "path": "^0.12.7"
  },
  "scripts": {
    "start": "node index.js",
    "heroku-postbuild": "cd client && npm install && npm run build"
  }
}

and my client/package.json:

  "name": "test-tailwind",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "@material-ui/core": "^4.12.3",
    "@material-ui/icons": "^4.11.2",
    "@tailwindcss/line-clamp": "^0.3.0",
    "@tailwindcss/typography": "^0.5.0",
    "@testing-library/jest-dom": "^5.16.1",
    "@testing-library/react": "^12.1.2",
    "@testing-library/user-event": "^13.5.0",
    "axios": "^0.24.0",
    "react": "^17.0.2",
    "react-dom": "^17.0.2",
    "react-markdown": "^7.1.2",
    "react-paginate": "^8.1.0",
    "react-router-dom": "^5.2.0",
    "react-scripts": "5.0.0",
    "tailwind-scrollbar-hide": "^1.1.7",
    "web-vitals": "^2.1.2"
  },
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },
  "eslintConfig": {
    "extends": [
      "react-app",
      "react-app/jest"
    ]
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  }
  
}

Please I really need deploy this app because building it has caused me sleepless nights and I can't just quit now. Link to github repo: https://github.com/Emabliss/joblisting. Thanks in advance.