@type t() ::
  %Stripe.Params.BillingPortal.SessionCreateParams.FlowData.SubscriptionUpdateConfirm{
    discounts:
      [
        Stripe.Params.BillingPortal.SessionCreateParams.FlowData.SubscriptionUpdateConfirm.Discounts.t()
      ]
      | nil,
    items:
      [
        Stripe.Params.BillingPortal.SessionCreateParams.FlowData.SubscriptionUpdateConfirm.Items.t()
      ]
      | nil,
    subscription: String.t() | nil
  }