Replacing embeds and returning to the view without saving to the database

I have a database object with an embeds_many that is defined as embeds_many :availability, Availability, on_replace: :delete. I am trying to replace it completely but putting new data with put_embed and returning the changeset to the view without saving it, but it is not working. I have this in my context:

def update(calendar, attrs) do
    calendar
    |> Calendar.changeset(attrs)
    |> Ecto.Changeset.put_embed(:availability, get_updated_availability())
end

and in the controller, I have something like

changeset = Calendars.update(calendar, calendar_params)
render(conn, "index.html", calendar: calendar, changeset: changeset)

when I try to process it, I get

%CombinaAi.Calendars.Availability{id: nil, weekday: nil, time_intervals: []}

which doesn’t render anything, but it works if I save it to the database before returning it to the view.

Is there a way to make this pipeline work without saving it to the database?