Hi Ida,
Currently its only possible to use in Brazil. They’re still testing it. However , if you live in Brazil you can start using by following these steps below.

1. Open the chat with whom you’d like to send money > tap Attach > Payment.
2. Tap CONTINUE on the Facebook Pay screen.
3. Tap CONTINUE to accept WhatsApp’s Payments Terms and Privacy Policy, Facebook’s Payments Terms and Privacy Policy, and Cielo’s Terms.
4. Create a 6-digit Facebook Pay PIN.
5. Confirm your Facebook Pay PIN by entering it again > tap NEXT.
6. To use your fingerprint instead of manually entering your PIN, tap USE FINGERPRINT. Otherwise, tap Skip to manually enter your PIN.
7. Enter your full legal first and last name and your CPF > tap Next .
8. Add your card information. This includes your debit card number, expiry date, and CVV.
9. Tap SAVE.
10. After your card information has been added, you can verify your card.