Apple has released watchOS 4.2 for the Apple Watch. The new software upgrade brings a number of changes, the most notable being support for Apple Pay Cash, a quick peer-to-peer payments system that is a direct competitor to Square Cash and Venmo.
As you might know, Pay Cash recently went live for iPhones and iPads through iOS 11.2. If you’d like to use it on your Apple Watch, you’ll first have to activate it on your phone or tablet. 
This is done by going to Settings > Wallet > Apple Pay. If you’re on iOS 11.2 and are living in a region where the service is available, you should see an Apple Pay Cash toggle. Enable it and, of course, make sure that you have money in your account.
Apple says that the patch is available to all Apple Watch models. Before proceeding with the update, make sure that your Apple Watch is on its charger and is at least 50 percent charged. Then, connect your iPhone to a Wi-Fi network and keep it close to the smartwatch until the process is complete.
source: Phonearena
