herokuにReact + node.js + postgresqlのアプリをデプロイしたい。

昨日からずっと、下記のエラーに苦しめられています。色々調べて考えられることは全てやりました。誰か助けてください。

2020-04-08T03:10:35.020938+00:00 heroku[router]: at=error code=H20 desc="App boot timeout" method=GET path="/" host=heroku-with-todos.herokuapp.com request_id=c70b705b-15c5-4c15-a31c-20311149ef1e fwd="119.106.99.159" dyno= connect= service= status=503 bytes= protocol=https
2020-04-08T03:10:35.114771+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=heroku-with-todos.herokuapp.com request_id=4206bc2c-91b4-4ceb-9159-94965c3f45b2 fwd="119.106.99.159" dyno= connect= service= status=503 bytes= protocol=https

サーバーサイドのリッスンポートもprocess.env.port | 3000にしました。
一応、下記がpackage.jsonです。

{
  "name": "react-todo-heroku",
  "version": "1.0.0",
  "engines": {
    "node": "^12.0.0"
  },
  "description": "",
  "main": "index.js",
  "scripts": {
    "server": "node src/server/server.js",
    "client": "webpack-dev-server --config ./config/webpack.config.dev.js --open --mode development",
    "build": "webpack --config ./config/webpack.config.dev.js --mode development",
    "dev": "NODE_ENV=development concurrently \"npm run client\" \"npm run server\"",
    "start": "NODE_ENV=production npm run build && npm run server",
    "lint": "eslint src --fix -c .eslintrc.json 'src/**/*.js'"
  },
  "dependencies": {
    "@material-ui/core": "^4.9.8",
    "axios": "^0.19.2",
    "dotenv": "^8.2.0",
    "express": "^4.17.1",
    "pg": "^8.0.0",
    "react": "^16.13.1",
    "react-dom": "^16.13.1"
  },
  "devDependencies": {
    "babel-cli": "^6.26.0",
    "babel-core": "^6.26.3",
    "babel-eslint": "^10.1.0",
    "babel-loader": "^7.1.5",
    "babel-preset-env": "^1.7.0",
    "babel-preset-es2015": "^6.24.1",
    "babel-preset-react": "^6.24.1",
    "concurrently": "^5.1.0",
    "css-loader": "^3.4.2",
    "eslint": "^6.8.0",
    "eslint-config-prettier": "^6.10.1",
    "eslint-plugin-prettier": "^3.1.2",
    "eslint-plugin-react": "^7.19.0",
    "html-webpack-plugin": "^4.0.4",
    "husky": "^4.2.3",
    "lint-staged": "^10.1.1",
    "nodemon": "^2.0.2",
    "prettier": "^2.0.2",
    "style-loader": "^1.1.3",
    "webpack": "^4.42.1",
    "webpack-cli": "^3.3.11",
    "webpack-dev-server": "^3.10.3",
    "webpack-merge": "^4.2.2"
  },
  "pre-commit": [
    "lint-staged"
  ],
  "lint-staged": {
    "*.{js, jsx}": [
      "eslint --fix"
    ]
  },
  "husky": {
    "hooks": {
      "pre-commit": "lint-staged"
    }
  }
}

Procifleでweb: npm startをしています。
あと、考えられるのはclientとserverの通信のさいのプロキシの設定が間違ってるかもしれません。

const merge = require("webpack-merge");
const webpackConfig = require("./webpack.config.js");

module.exports = merge(webpackConfig, {
  mode: "development",
  devServer: {
    host: "https://example.herokuapp.com",
    proxy: {
      "/api": {
        target: "https://example.herokuapp.com:" + process.env.PORT,
      },
    },
  },
});