protocol Enumerable not implemented for #Ash.Changeset

defmodule Telepai.App.Session do
  attributes do
    integer_primary_key(:id)
    attribute :external_id, :string
    attribute :settings, :string
  end

  actions do
    defaults([:create, :read, :update, :destroy])

    create :new do
      accept([:settings])

      change(fn changeset, _ ->
        now = NaiveDateTime.utc_now() |> NaiveDateTime.to_string()
        external_id = now |> HumanReadableIdentifierGenerator.fetch_human_readable_id!()

        changeset |> Ash.Changeset.change_attribute(:external_id, external_id)
      end)
    end
  end

  code_interface do
    define_for(__MODULE__)
    define(:new)

    # Note: if I don't define :create, compiler complains that 
    # `create/2` and `create!/2` are private or not defined
    define(:create)
  end
end

> Telepai.App.Session.new!(%{settings: "aaa"})
protocol Enumerable not implemented for #Ash.Changeset<action_type: :create, action: :new, attributes: %{external_id: "pingo-frangimini-51", settings: "aaa"}, relationships: %{}...
...
    (ash 2.6.27) lib/ash/changeset/changeset.ex:998: Ash.Changeset.cast_params/3
    (ash 2.6.27) lib/ash/changeset/changeset.ex:747: Ash.Changeset.do_for_action/4
    (telepai 0.1.0) lib/ash/code_interface.ex:533: Telepai.App.Session.create!/2