How do I send someone money using Apple Pay

Please follow the steps in the support article linked below.

>>On your iPhone or iPad

1. Open the Messages app, then start a new conversation or tap an existing one.
2. Tap the Apple Cash button . If you don't see the Apple Cash button, tap  first.
3. Enter the amount that you want to send.
4. Tap Send, then tap the Send button  to review or cancel the payment.
5. Confirm your payment with Face ID, Touch ID, or your passcode.<<

If the person you sent money to has not accepted the money yet, you can cancel the payment.

Send and receive money with Apple Cash - Apple Support