Apple Pay cash has been introduced by Apple for iPhones, iPads on iOS 11.2 and for Apple watch on Watch OS 4.2. Apple Pay Cash is limited to US alone. Apple has released an animated video showing you how to send and receive money using the Pay Cash. Apple Pay Cash allows you to make and receive payments on a peer-to-peer basis while using the iMessage application. If you use a debit card to make a payment, there is no charge. Apple will add a 3% fee if you use a credit card to send money.
To use this feature both the parties should have updated to latest version (iOS and watch OS) in the respective device to enable Pay Cash. Money, you receive will be added to the Apple Pay Cash card in your Apple Wallet. From there, you can send your Apple Pay Cash balance to a connected bank account. A balance can also be used to pay for transactions inside a store or online using Apple Pay.