FIDO2 WebAuthn 2FA problem - Webauth Error: NotAllowed Error

I am new to BW and am so far loving being able to set this up on my own NAS. I am running the docker image on Synology, and have it all running fine but am struggling with 2FA.

I have managed to get OTP working fine via a yubikey, however trying to setup FIDO2 I am having problems. Setting it up in the 2FA menu works fine, but when I try to login with it I am getting the error

“An error has occurred”
WebAuth Error: NotAllowedError: The operation either timed out or was not allowed."

If anyone could give me some pointers on where to start looking this would be greatly appreciated!