Apple has launched Apple Pay Cash in iOS 11.2 beta 2. This means the peer-to-peer payments service will be availble whenever iOS 11.2 is made public. Apple Pay Cash allows iOS users to send payments to other iOS users through the Messages app.
You can set up Apple Pay Cash through the Wallet app. To set up Apple Pay Cash, open the Wallet app on your device, then tap the Apple Pay Cash card. Follow the prompts and confirm your information once you're redirected to the Settings app. Once your information is confirmed you will be able to access Apple Pay Cash through your Wallet app.