Merchant Category Code (MCC) Group. The MCC is a four-digit number used by the Card Schemes to define the trading category of the merchant. The MDES platform is used in iPhone 6, iPhone 6 Plus and Apple Watch to enable secure payments to take place for contactless and in-app payments. You can configure your cards to allow/disallow payments based on the merchant's MCC. For more information, see the Key Concepts Guide.