At the top of page 12, after “Now, start the web server,” the book shows sample output, but does not show the command to start the web server. I used mix phx.server.

On my Windows 11 development PC, this yields the following warning and debug messages:

D:\Users\Joel\Documents\Projects\pento>mix phx.server
[warning] Phoenix is unable to create symlinks. Phoenix' code reloader will
run considerably faster if symlinks are allowed. On Windows, the lack of
symlinks may even cause empty assets to be served. Luckily, you can
address this issue by starting your Windows terminal at least once with
"Run as Administrator" and then running your Phoenix application.
[info] Running PentoWeb.Endpoint with cowboy 2.10.0 at 127.0.0.1:4000 (http)
[info] Access PentoWeb.Endpoint at http://localhost:4000
[watch] build finished, watching for changes...

Rebuilding...

Done in 297ms.
[debug] Plug.Session could not verify incoming session cookie. This may happen when the session settings change or a stale cookie is sent.
[info] CONNECTED TO Phoenix.LiveView.Socket in 102┬╡s
  Transport: :websocket
  Serializer: Phoenix.Socket.V2.JSONSerializer
  Parameters: %{"_csrf_token" => "K2pUXlM_GRk4JAkEEGIxQTEcCz47GW4Fe28jboIIATjK_QV2FhEJKX_O", "_live_referer" => "undefined", "_mounts" => "0", "_track_static" => %{"0" => "http://localhost:4000/assets/app.css", "1" => "http://localhost:4000/assets/app.js"}, "vsn" => "2.0.0"}
[info] GET /guess
[debug] ** (Phoenix.Router.NoRouteError) no route found for GET /guess (PentoWeb.Router)
    (pento 0.1.0) deps/phoenix/lib/phoenix/router.ex:487: PentoWeb.Router.call/2
    (pento 0.1.0) lib/pento_web/endpoint.ex:1: PentoWeb.Endpoint.plug_builder_call/2
    (pento 0.1.0) deps/plug/lib/plug/debugger.ex:136: PentoWeb.Endpoint."call (overridable 3)"/2
    (pento 0.1.0) lib/pento_web/endpoint.ex:1: PentoWeb.Endpoint.call/2
    (phoenix 1.7.7) lib/phoenix/endpoint/sync_code_reload_plug.ex:22: Phoenix.Endpoint.SyncCodeReloadPlug.do_call/4
    (plug_cowboy 2.6.1) lib/plug/cowboy/handler.ex:11: Plug.Cowboy.Handler.init/2
    (cowboy 2.10.0) d:/Users/Joel/Documents/Projects/pento/deps/cowboy/src/cowboy_handler.erl:37: :cowboy_handler.execute/2
    (cowboy 2.10.0) d:/Users/Joel/Documents/Projects/pento/deps/cowboy/src/cowboy_stream_h.erl:306: :cowboy_stream_h.execute/3
    (cowboy 2.10.0) d:/Users/Joel/Documents/Projects/pento/deps/cowboy/src/cowboy_stream_h.erl:295: :cowboy_stream_h.request_process/3
    (stdlib 4.3.1) proc_lib.erl:240: :proc_lib.init_p_do_apply/3

Following the instructions in the warning message, I opened a “Run as Administrator” command window and executed mix phx.server from the pento directory. After that, I was able to run mix phx.server from an ordinary command window without any problems.