Sent Apple Cash payment only to discover it was all a scam

See the following from Send and receive money with Apple Cash - Apple Support

How to cancel or dispute a payment

1. Open the Messages app, then open the conversation and tap the payment.
2. Your Apple Cash card will open in the Wallet app. Under Latest Transactions, tap the payment, then tap it again.
3. Tap Cancel Payment.

If you don't see Cancel Payment, the person has already accepted the payment. Try asking the recipient to send the money back to you instead.

It might take 1-3 business days for the money to be refunded, depending on your bank or card issuer.

Apple Cash person to person payments are just like any other private transaction between two people, so only send and receive money with people you know. If you have questions or concerns about a transaction, please contact us.

Sorry, but what FoxFifth linked to and copy and pasted is exactly what you need to do.

How to cancel or dispute a payment

1. Open the Messages app, then open the conversation and tap the payment.
2. Your Apple Cash card will open in the Wallet app. Under Latest Transactions, tap the payment, then tap it again.
3. Tap Cancel Payment.

If you don't see Cancel Payment, the person has already accepted the payment. Try asking the recipient to send the money back to you instead.

If you want to call Apple Support, please call 1-800-MY-APPLE.