https://arstechnica.com/gadgets/2017/12/apple-pay-cash-hits-apple-watches-with-watchos-4-2-release/

The latest software update for Apple Watch is now available, just a few days after Apple released iOS 11.2 earlier than expected. The biggest link between the iDevice and Watch software updates is Apple Pay Cash, which is now available for Apple's wearable in watchOS 4.2