How to deploy Uppy companion app to Firebase

Question

This migth be silly question but I have very little knowledge of node.js, firebase and devops at overall.

I'm trying to host Uppy Companion app in the Firebase hosting: https://uppy.io/docs/companion/#Options

App works locally, I can deploy it to Firebase but can't access endpoint. I guess the problem is with the config and the host url or some firebase settings I'm not aware of. That's the index.js of app:

const bodyParser = require("body-parser");
const session = require("express-session");
const companion = require("@uppy/companion");

const app = express();

app.use(bodyParser.json());
app.use(
  session({
    secret: "some-secret",
    resave: true,
    saveUninitialized: true,
  })
);

app.use((req, res, next) => {
  res.setHeader("Access-Control-Allow-Origin", req.headers.origin || "*");
  next();
});

// Routes
app.get("/companion", (req, res) => {
  res.setHeader("Content-Type", "text/plain");
  res.send("Welcome to Companion");
});

// initialize uppy
const companionOptions = {
  providerOptions: {
    drive: {
      key: "google drive key",
      secret: "google drive secret",
    },
  },
  server: {
    host: "localhost:3020",
    protocol: "http",
  },
  filePath: "./output",
  secret:"secret",
  debug: true,
};

const { app: companionApp } = companion.app(companionOptions);
app.use(companionApp);

// handle 404
app.use((req, res) => {
  return res.status(404).json({ message: "Not Found" });
});

// handle server errors
app.use((err, req, res) => {
  console.error("\x1b[31m", err.stack, "\x1b[0m");
  res.status(err.status || 500).json({ message: err.message, error: err });
});

companion.socket(app.listen(3020));

console.log("Welcome to Companion!");
console.log(`Listening on http://0.0.0.0:${3020}`);

But after deployment when I'm trying access the endpoint I get:

Can someone point me to the direction how to fix this? I guess the problem is with my configuration, not the Firebase itself.

Thanks!