@type t() :: %PolarExpress.Schemas.CustomerStateSubscription{
  amount: integer() | nil,
  cancel_at_period_end: boolean() | nil,
  canceled_at: DateTime.t() | nil,
  created_at: DateTime.t() | nil,
  currency: String.t() | nil,
  current_period_end: DateTime.t() | nil,
  current_period_start: DateTime.t() | nil,
  custom_field_data:
    %{
      required(String.t()) =>
        String.t() | integer() | boolean() | DateTime.t() | nil
    }
    | nil,
  discount_id: String.t() | nil,
  ends_at: DateTime.t() | nil,
  id: String.t() | nil,
  metadata: PolarExpress.Schemas.MetadataOutputType.t() | nil,
  meters: [PolarExpress.Schemas.CustomerStateSubscriptionMeter.t()] | nil,
  modified_at: DateTime.t() | nil,
  product_id: String.t() | nil,
  recurring_interval:
    PolarExpress.Schemas.SubscriptionRecurringInterval.t() | nil,
  started_at: DateTime.t() | nil,
  status: String.t() | nil,
  trial_end: DateTime.t() | nil,
  trial_start: DateTime.t() | nil
}