How can I do a better code and architecture design with Elixir Erlang and FP principles

Hi, I’ve been developing a project for a few months and since the beginning i’ve been paying attention to the design of my code, writing it modular, well separated and those kind of things, but it’s been growing and i’m missing something I dont really know what. I’m often kind of lost of what a module or service returns, you now like when a module calls a module that calls a module that calls another module, and I caught myself open a few archives to check the returns. I think what is missing for me it’s some kind of architecture guide, something like interfaces to know exactly what x or y returns, so I’m here asking for some general or personal resources into that.
To give an example, I have the a controller that at some point calls another module

defp handle_answer(%{"payload" => payload, "status" => status, "meta" => meta}) when is_boolean(status) do
    case status do
      true -> handle_paid_pix(payload)
      false -> handle_failure_pix(payload, meta)
    end
  end

  defp handle_answer(_), do: {:error, FE.initerror("validation", "invalid payload")}

  defp handle_paid_pix(payload), do: TransactionRealm.handle_pix_paid(payload)
  defp handle_failure_pix(payload, meta), do: TransactionRealm.handle_pix_failed(payload, meta)

but then in this module I got more calls to another modules

 def handle_pix_paid(payload) do
    PixTransaction.handle_pix_paid(payload)
  end

  def handle_pix_failed(payload, meta) do
    PixTransaction.handle_failure_pix(payload, meta)
  end

    def handle_pix_paid(payload) do
        with {:ok, _} <- MnesiaPendingContractsDomain.update_payment_status({:payload,  payload, :pix_paid}),
            {:ok, _} <- EctoContractsDomain.update_payment_status({:payload, payload, :pix_paid}) do
            :ok
        else
            {:error, _} = error -> error
        end
    end

    def handle_failure_pix(payload, meta) do
        with {:ok, _} <- MnesiaPendingContractsDomain.update_contract_meta({:payload, payload, meta}) do
            :ok
        else
            {:error, _} = error -> error
        end
    end

I dont know if its on my mind but really feels like a terrible spagetthi code terrible typed and error prone. As I said at the beginnig designing that way was no problem, but i’m really a constraint that ties my code which makes it cohesive and well-fitted. Sorry if it’s a very abstract question, I tried to explain it as best I could.