Unmet dependencies don't fail yarn install but may cause runtime issues?

Question

Heroku

The react app successfully deployed to Heroku, but when you open the link it says: Application error. and the error is:
! This app may not specify any way to start a node process
https://devcenter.heroku.com/articles/nodejs-suppo...
! Unmet dependencies don't fail yarn install but may cause runtime
issues
here is package.json

"@testing-library/jest-dom": "^5.11.4",
    "@testing-library/react": "^11.1.0",
    "@testing-library/user-event": "^12.1.10",
    "axios": "^0.21.1",
    "body-parser": "^1.19.0",
    "bootstrap": "^5.0.1",
    "cors": "^2.8.5",
    "express": "^4.17.1",
    "findup-sync": "^0.1.2",
    "fontello-cli": "^0.6.2",
    "mdbreact": "^5.0.2",
    "react-animated-slider": "^2.0.0",
    "react-bootstrap": "^1.6.1",
    "react-dom": "^17.0.2",
    "react-redux": "^7.2.4",
    "react-scripts": "4.0.3",
    "redux": "^4.1.0",
    "redux-devtools-extension": "^2.13.9",
    "redux-thunk": "^2.3.0",
    "web-vitals": "^1.0.1"
  },
  "scripts": {
    "client": "react-scripts start",
    "server": "nodemon server/server.js",
    "dev": "concurrently \"yarn run client\" \"yarn run server\"",
    "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"
    ]
  },
  "devDependencies": {
    "concurrently": "^6.2.0",
    "nodemon": "^2.0.7"
  }
}