The biometric data never leaves your device. Your biometric is only used to unlock a private key stored in the secure enclave of your phone. This private key is

The biometric data never leaves your device. Your biometric is only used to unlock a private key stored in the secure enclave of your phone. This private key is then used to sign a server-sent challenge. The phone sends this signed challenge back to the server, where the server can validate it using the public key. The public/private key gets generated by the phone upon first registration with the server.