Heroku H10 works on localhost, won't work in deployment

This error seems to be pretty popular here! The app works great locally, but when deploying to Heroku... crickets, Application crashes.

This is server.js

var app = express();
var PORT = process.env.PORT || process.env.REACT_APP_PORT;
app.use(express.urlencoded({ extended: true }));
app.use(express.json());

(process.env.NODE_ENV === "production") ? app.use(express.static("build")) : app.use(express.static("public"));

//code goes here

app.use(cors());

app.get('*', function (req, res) {
    res.redirect('api/tweets');
})

app.get('api/tweets', function (req, res) {
    tweetData.findOne({}, [], { $orderby : { 'created_at' : -1 } }, function(err, post) {
        console.log(post);
        res.send(post);
    });
});

app.listen(PORT, function() {
    console.log("App running on port " + PORT);
});

This is log entry

2020-05-10T00:12:59.057966+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=quarantine-life.herokuapp.com request_id=bd00538a-e6c4-4d33-ab5b-957eca72146f fwd="68.173.68.75" dyno= connect= service= status=503 bytes= protocol=https

This is the API call in App.js

  callTwitterApi = async () => {
    await axios.get(my_heroku_app_URL_goes_here)
      .then(res => {
          //pipeline length control
          if (this.state.count === 20){ 
            this.clearTweets();
          }
          //checking if the tweet is new
          this.checkIfNew(res.data);
      })
      .catch (error => {
        this.setState({ error, isLoading: true });
      })
      this.setState({isLoading: true, isNew: ""});
  }

Package.json:

`{
  "name": "quarantine-life",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "@testing-library/jest-dom": "^4.2.4",
    "@testing-library/react": "^9.5.0",
    "@testing-library/user-event": "^7.2.1",
    "axios": "^0.19.2",
    "bootstrap": "^4.4.1",
    "cors": "^2.8.5",
    "dotenv-webpack": "^1.7.0",
    "express": "^4.17.1",
    "gh-pages": "^2.2.0",
    "http-proxy-middleware": "^1.0.3",
    "mongo": "^0.1.0",
    "mongoose": "^5.9.10",
    "morgan": "^1.10.0",
    "nodemon": "^2.0.3",
    "react": "^16.13.1",
    "react-animated-css": "^1.2.1",
    "react-bootstrap": "^1.0.1",
    "react-dom": "^16.13.1",
    "react-scripts": "3.4.1",
    "react-transition-group": "^4.4.0",
    "twitter": "^1.7.1"
  },
  "scripts": {
    "start": "react-scripts start & node server.js",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },
  "eslintConfig": {
    "extends": "react-app"
  },
  "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": "^5.2.0",
    "dotenv": "^8.2.0"
  },
  "proxy": "HEROKU_URL_GOES_HERE"
}
`

I've tried the following approaches

• proxy entry onto package.json
• middleware npm package
• ungodly amount of beer

Any help for this noob right here, greatly appreciated!