I set up FIDO2 2FA for this website and when tried to log in, i get "Unknown error". Please Help!

I set up 2FA with my Nitrokey 3 for this website: support.nitrokey.com (just with nitrokey, no OTP or backup codes were required from me to enable this). When I tried to log back in, I got “Unknown Error”.

Basically I’m locked out from my account.
Please Help!

Thank you very much. Best regards.