## TL;DR

This is an upstream 1Password bug, not your library: the 1Password Chrome extension intercepts the WebAuthn call and replaces it with its own implementation, which throws `Illegal invocation`. Chrome 129 added PublicKeyCredential features that exposed the incompatibility. Track the 1Password fix; as a workaround, register the passkey without the 1Password extension intercepting.

## The error

```text
Uncaught TypeError: Illegal invocation
```

Shown in the UI when registering a FIDO2 credential with a 1Password passkey, at the `navigator.credentials.create` / WebAuthn call in the client code.

## Fix it

1. Confirm the scope: the error happens only when the 1Password passkey flow is used, not with platform authenticators.
   Success check: other passkey providers register fine.

2. Workaround: disable the 1Password extension's passkey interception (or use a different browser/profile) and retry registration.
   Success check: registration completes with no Illegal invocation.

3. Track the upstream 1Password fix for full resolution.
   Success check: re-enable the extension after the fix and registration works.

## When this applies

- `Illegal invocation` on FIDO2 credential registration with 1Password passkeys.
- Chrome 129+.

## When it does not apply

- Other authenticators fail too; that is a problem in your WebAuthn code.
- Different WebAuthn errors (NotAllowedError, InvalidStateError).
- The error occurs outside credential registration.

## Compatibility

- Chrome 129+ (PublicKeyCredential additions exposed the bug). 1Password Chrome extension passkey implementation.
- Library: amazon-cognito-passwordless-auth client (fido2.ts).

## Variant phrasings

- 1Password passkey Illegal invocation
- Uncaught TypeError Illegal invocation webauthn
- fido2 register Illegal invocation 1password

## Why it happens

The 1Password extension replaces the native WebAuthn implementation with its own. Its replacement does not handle the newer PublicKeyCredential surface Chrome 129 added, so the call throws `Illegal invocation` instead of completing.

## Edge cases

- Users on older Chrome may not hit it; the incompatibility is version-specific.
- Source: https://github.com/aws-samples/amazon-cognito-passwordless-auth/issues/94