The put_flash/3 docs include the following notes that seem relevant:

Note: While you can use put_flash/3 inside a Phoenix.LiveComponent, components have their own @flash assigns. The @flash assign in a component is only copied to its parent LiveView if the component calls push_navigate/2 or push_patch/2.

Note: You must also place the Phoenix.LiveView.Router.fetch_live_flash/2 plug in your browser’s pipeline in place of fetch_flash for LiveView flash messages be supported, for example:

import Phoenix.LiveView.Router

pipeline :browser do
  ...
  plug :fetch_live_flash
end

For the modal that does not work, what happens is that when you submit the form, it crashes the component and the live view, because you are expecting a “ticket_id” parameter but none is submitted. You should see reports that the LiveView crashed both in your browser console (run liveSocket.enableDebug() once) and your app console.

If I change the handle_event to this:

  def handle_event("save", %{"invite_ticket_form" => _}, socket) do
      {:noreply,
       socket
       |> assign(:open_modal, false)
       |> assign(:status, :success)
       |> put_flash(:info, gettext("Invitation sent"))
       |> push_redirect(to: "/events/#{socket.assigns.event.slug}/edit/attendees")}
  end

Then it works for me (in that the flash shows).

oh, I think you were right! there was an error and I didn’t see it. I will be do some tests tomorrow but I think the mistery is solved