Flat rate and metered usage

Section

defmodule StripeSubscription do
  alias Stripe.{Plan, Subscription}

  def create_flat_rate_price(product_id) do
    flat_rate =
      Plan.create(%{
        # $1,000 in cents
        amount: 100_000,
        currency: "usd",
        interval: "month",
        product: product_id
      })

    flat_rate
  end

  def create_tiered_price(product_id) do
    tiered_price =
      Plan.create(%{
        currency: "usd",
        product: product_id,
        interval: "month",
        billing_scheme: "tiered",
        usage_type: "metered",
        tiers_mode: "volume",
        tiers: [
          %{up_to: "inf", unit_amount: 4}
        ]
      })

    tiered_price
  end

  def create_subscription(flate_rate_price_id, tiered_price_id, customer_id) do
    case Subscription.create(%{
           customer: customer_id,
           items: [%{price: flate_rate_price_id}, %{price: tiered_price_id}]
         }) do
      {:ok, subscription} -> subscription
      {:error, reason} -> IO.puts("Stripe Error: #{reason}")
    end
  end
end

customer_id = "cus_FJqsEj8guLgsw7"
product_id = "prod_FVP32YJFf8FEs7"
{:ok, flat_rate} = StripeSubscription.create_flat_rate_price(product_id)
{:ok, tiered_plan} = StripeSubscription.create_tiered_price(product_id)
tiered_plan

subscription = StripeSubscription.create_subscription(flat_rate.id, tiered_plan.id, customer_id)

params = %{quantity: 1000, timestamp: :os.system_time(:second), action: "increment"}

[item1, tiered_item] = subscription.items.data
tiered_item

Stripe.SubscriptionItem.Usage.create(tiered_item.id, params)