gettext.extract not extracting strings

I’m likely missing something here. When I run:

mix gettext.extract

it just generates a file with a few default strings from core components like “Actions” and “Attempting to reconnect”.

I created a Backend as per the Github page like such:

ct@mt:~/path/to/file$ cat lib/myapp/gettext.exdefmodule MyApp.Gettext douse Gettext.Backend, otp_app: :my_append

And just for testing:

defmodule MyAppWeb.EscortLive.Index do
  use MyAppWeb, :live_view
  use Gettext, backend: MyApp.Gettext

  @impl true
  def mount(_params, _session, socket) do
    gettext("A simple test")
#...
end

But that string doesn’t get picked up. Also tried in other files with no result.