I am working on implementing merchant token notifications. When calling this endpoint https://developer.apple.com/documentation/merchanttokennotificationservices/merchant-token-event-retrieval, the result contains a CardMetadata object with an expirationDate field (see https://developer.apple.com/documentation/merchanttokennotificationservices/cardmetadata). What is the format of this field? The spec only mentions that it has a maximum length of 8 characters.
