What would you guys think is the best way to handle a signup form that includes making a payment?

I was thinking of a Registration.changest where the module looks like

defmodule App.Store.Registration do
  use Ecto.Schema

  import Ecto.Changeset
  import App.Repo, only: [preload: 1]

  alias App.Accounts.User

  schema "registrations" do
    belongs_to :customer, App.Store.Customer
    belongs_to :purchase, App.Store.Purchase
    belongs_to :user, App.Accounts.User
    timestamps()
  end

  def register_changeset(%__MODULE__{} = registration, attrs) do
    registration
    |> preload([:customer, :purchase])
    |> cast(attrs)
    |> cast_assoc(:customer, required: true)
    |> cast_assoc(:purchase, required: true)
  end

  def complete_changeset(%__MODULE__{} = registration, attrs) do
    registration
    |> preload(:user)
    |> cast(attrs)
    |> cast_assoc(:user, required: true, with: &User.register_changeset/2)
  end
end

Where you first complete a form that corresponds to register_changeset and then once that is done and the payment is processed show a form for the complete_changeset to create the user account w/ password, etc.

So, for the payment part, I was thinking App.Customer would have a payment_method field which would be an embed, or assoc or something that included a stripe token that is generated as part of filling out the signup form payment details.

Does this seem like a good way to do it? If not, what would you do?

Where would you guys put the payment processing step?

If the payment failed, I’d like to return a changeset error ideally, since then the response would all be the same no matter the error, but then we have the issue of a possible succeeding payment but an invalid changeset overall. therefore we could have a resubmission and possible double-charge.