One payment method applied to the receipt.
@type payment_type() :: :card | :cash | :gift_card
@type t() :: %Monzo.Receipt.Payment{ aid: String.t() | nil, amount: integer(), auth_code: String.t() | nil, bin: String.t() | nil, currency: String.t(), gift_card_type: String.t() | nil, last_four: String.t() | nil, mid: String.t() | nil, tid: String.t() | nil, type: payment_type() }