Open the Messages app on your iPhone
Start or open a conversation with the person you want to pay
Tap the Apple Pay button in the app drawer above the keyboard
Enter the amount you want to send
Tap Pay
Authenticate with Face ID, Touch ID, or your passcode
Confirm the payment
Make sure both you and the recipient have Apple Cash set up and are in a supported region
If Apple Pay is not available in Messages, update iOS and check that Apple Cash is enabled in Wallet settings