OptionalamountDecimal string, e.g. "9.99".
OptionalcurrencyISO-4217 three-letter code, e.g. "USD".
OptionaleventOptionalidentityOptionaloccurredISO-8601 override; defaults to the call-time timestamp.
OptionalproductOptionalsubscriberDefaults to the current scope (app user id, else anonymous id).
Optional fields for track.
eventTypeis the first positional arg.