Problem hosting Nuxt.js SSR app on Firebase

I'm trying to host a Nuxt.js app on Firebase, and I've followed this tutorial, and I got stuck at #10, when trying to do sudo firebase serve --only functions, hosting. I kept getting this Timed out waiting for function to respond..

Upon further investigating I found out that the problem is in /functions/index.js. The line nuxt.renderRoute('/').then(...) is taking forever to run, because the console.log('After render') is never called. Here's how the /functions/index.js looks like

/functions/index.js

const functions = require('firebase-functions')
const express = require('express')
const { Nuxt } = require('nuxt')

const app = express()

const config = {
  dev: false,
  buildDir: 'nuxt',
  build: {
    publicPath: '/public/'
  }
}
const nuxt = new Nuxt(config)

app.get('**', function (req, res) {
  res.set('Cache-Control', 'public, max-age=600, s-maxage=1200')
  console.log('it still works here')

  nuxt.renderRoute('/').then(result => {
    console.log(result.html)
    res.send(result.html)
  }).catch(e => {
    console.log(e)
    res.send(e)
  })
  console.log('After render')
})

module.exports.nuxtApp = functions.https.onRequest(app)

And this is how my terminal output looks like:

from Problem hosting Nuxt.js SSR app on Firebase