`mix phx.server` does not work on PROD but works on DEV

Background

I am toying with PhoenixLiveView a little and I have my demo app ready to go. When I test it in DEV, it all works wonders. But if I run MIX_ENV=prod mix phx.server then the page doesn’t even load.

Code

I am aware both my config/dev and config/prod differ significantly, therefore I can only assume the issue is in my config/prod. However, being a first time user of this framework, I don’t just want to replicate my config/dev file into the prod one, I actually want to know what is missing so I can fix it.

config/dev:

import Config

config :demo, DemoWeb.Endpoint,
  http: [port: 4000],
  debug_errors: true,
  code_reloader: true,
  check_origin: false,
  watchers: [
    node: [
      "node_modules/webpack/bin/webpack.js",
      "--mode",
      "development",
      "--watch-stdin",
      cd: Path.expand("../assets", __DIR__)
    ]
  ]

# Watch static and templates for browser reloading.
config :demo, DemoWeb.Endpoint,
  live_reload: [
    patterns: [
      ~r"priv/static/.*(js|css|png|jpeg|jpg|gif|svg)$",
      ~r"priv/gettext/.*(po)$",
      ~r"lib/demo_web/(live|views)/.*(ex)$",
      ~r"lib/demo_web/templates/.*(eex)$"
    ]
  ]

# Do not include metadata nor timestamps in development logs
config :logger, :console, format: "[$level] $message\n"

# Set a higher stacktrace during development. Avoid configuring such
# in production as building large stacktraces may be expensive.
config :phoenix, :stacktrace_depth, 20

# Initialize plugs at runtime for faster development compilation
config :phoenix, :plug_init_mode, :runtime

config.prod:

import Config

config :demo, DemoWeb.Endpoint,
  url: [host: "localhost", port: 80],
  cache_static_manifest: "priv/static/cache_manifest.json"

# Do not print debug messages in production
config :logger, level: :info

Questions

1. What is missing in my prod configuration?

If this is not the issue … than I am more lost than I initially thought. For those of you curious enough, here is the project:

https://github.com/Fl4m3Ph03n1x/live_view_demo