Did you enter a name for the device and click the “Add” button next to the input field after setting up the WebAuthn device?
And this might be a silly question, but did you specify a username when you tried to log in with the decice? Obviously, it must be the username of the account for which you have set up passwordless authentication. If you leave the username field blank or if you enter an incorrect username, you will get this message.
If the answer to the above questions is yes we would need more details about your setup to be able to help, and please take a look at the log to see if there are any error messages, and then post them here as well.