Call of Duty Warzone is a free to play game. It's not on GamePass and it doesn't need Xbox Live Gold either. MW2 and its multiplayer component is not free. You need to buy it if you want to play the single player game or MW2 multiplayer.
COD is a payment method by which the consignee or receiver of the shipment pays the driver or deliverer of the shipment. In a shipping collect situation, the receiver would simply pay the carrier.