I'm testing PRF evaluation with a YubiKey Bio through AuthenticationServices on iOS. Registration succeeds, but during later authentication with the enrolled fingerprint, I don't receive a PRF result. Using the key’s FIDO2 PIN works. Environment iPhone 12 iOS 27.0.1 YubiKey Bio connected through USB Firmware: 5.7.0 Steps to reproduce Configure a FIDO2 PIN and enroll a fingerprint on the YubiKey Bio. Connect the key to the iPhone. Register a credential using ASAuthorizationSecurityKeyPublicKeyCredentialProvider with PRF support requested. Request authentication for the registered credential with PRF input and userVerificationPreference = .required. Authenticate using the enrolled fingerprint. Check the returned PRF result. Compare this with authentication using the FIDO2 PIN. Expected result Successful authentication with PRF evaluation returns a 32-byte PRF output. Actual result No PRF result is returned when using fingerprint verification. The PIN flow works. Related report I found WebKit bug #314934, which reports missing PRF results with a YubiKey C Bio in Safari. The reporter observed successful authentication but a null PRF output. Could AuthenticationServices be affected by a similar issue? Is there a known limitation or workaround for PRF evaluation with YubiKey Bio fingerprint verification?