Issues getting data assigned in changeset

form.ex

defmodule FhForm.Form do
  use FhForm.Web, :model

  @required_fields ~w(name)a
  @optional_fields ~w(redirect_location success_message)a

  schema "forms" do
    field :name, :string
    field :redirect_location, :string
    field :success_message, :string
    field :url_iden, Ecto.UUID

    has_many :form_responses, FhForm.FormResponse

    timestamps()
  end

  @doc """
  Builds a changeset based on the `struct` and `params`.
  """
  def changeset(struct, params \\ %{}) do
    struct
    |> cast(params, @required_fields, @optional_fields)
    |> validate_required(@required_fields)
  end

  def create_changeset(struct, params \\ %{}) do
    struct
    |> changeset(params)
    |> put_random_form_identifier()
  end

  defp put_random_form_identifier(changeset) do
    case changeset do
      %Ecto.Changeset{valid?: true} ->
        put_change(changeset, :url_iden, Ecto.UUID.generate())
      _ ->
        changeset
    end
  end
end

form_response.ex

defmodule FhForm.FormResponse do
  use FhForm.Web, :model

  @required_fields ~w{data}a
  @optional_fields ~w{ip_address referrer}a

  schema "form_responses" do
    field :ip_address, :string
    field :referrer, :string
    field :data, :map
    belongs_to :form, FhForm.Form

    timestamps()
  end

  @doc """
  Builds a changeset for forms submitted through the HTML form-data API
  """
  def api_html_changeset(struct, params \\ %{}) do
    struct
    |> assign_params_to_data(params)
    |> cast(params, @required_fields, @optional_fields)
    |> validate_required(@required_fields)
  end

  defp assign_params_to_data(%Ecto.Changeset{} = cs, params) do
    put_change(cs, :data, params)
  end
  defp assign_params_to_data(cs, _params), do: cs
end

FormResponseController.ex

defmodule FhForm.API.HTML.FormResponseController do
  use FhForm.Web, :controller

  alias FhForm.Form
  alias FhForm.FormResponse

  def create(conn, params) do
    IO.inspect params
    form = Repo.get_by(Form, url_iden: params["url_identifier"])
    changeset =
      form
      |> build_assoc(:form_responses)
      |> FormResponse.api_html_changeset(params)

    case Repo.insert(changeset) do
      {:ok, _form_response} ->
        conn
        |> redirect(to: form_response_path(conn, :success, params["url_identifier"]))
      {:error, changeset} ->
        IO.inspect changeset
        conn
        |> send_resp(500, "Oops, something went wrong!")
    end
  end

  def success(conn, _) do
    render(conn, "success.html")
  end
end