In my lib/myapp/application.ex file I set up a Registry and I give it the name :myapp_registry:

  def start(_type, _args) do
    children = [
      # Start the Ecto repository
      MyApp.Repo,
      # Start the Telemetry supervisor
      MyAppWeb.Telemetry,
      # Start the PubSub system
      {Phoenix.PubSub, name: MyApp.PubSub},
      # Start the Endpoint (http/https)
      MyAppWeb.Endpoint,
      {Registry, [keys: :unique, name: :myapp_registry]},
      # , Start a worker by calling: MyApp.Worker.start_link(arg)
      # {MyApp.Worker, arg}
    ]

    # See https://hexdocs.pm/elixir/Supervisor.html
    # for other strategies and supported options
    opts = [strategy: :one_for_one, name: MyApp.Supervisor]
    Supervisor.start_link(children, opts)
  end

Then, in another module, when some event happens, I try and see what keys are in my registry:

IO.inspect(Registry.keys(:myapp_registry, self()))

But I get an error:

(ArgumentError) unknown registry: :myapp_registry

So… how do I start a Registry in my Phoenix application supervision tree and give it a name such that I can find and use my Registry later?