Captcha V2 failed

Question

I have read this post here https://www.chronoengine.com/forums/posts/t103681/chronoforms-6-recaptcha-no-captcha-passing-the-test-but-showing-error-you-didnt-pass-the-nocaptcha-verification?startat=20 and couldn't answer to it, so I open a new one. I think I have the same problem, and have followed the steps there.

I added a debugger which returns the error "timeout-or-duplicate" - am I right thinking that I do not need a server side captcha check, as this will challenge the same captcha twice? I am using AJAX Submit, so maybe that's why. I'll disable the server side check for now, but it would be great to know.

In my debugger, it says this:

Array
(
    [submit_google_nocaptcha] => Array
        (
            [response] => Array
                (
                    [success] => 1
                    [challenge_ts] => 2020-01-27T23:30:15Z
                    [hostname] => xxxxxx.ch (masked)
                )

            [_success] => The NoCaptcha verification was successfull.
            [var] => 1
        )

    [submit_validate_fields] => Array
        (
            [log] => Automatic validation enabled.
            [var] => 1
        )

    [google_nocaptcha17] => Array
        (
            [response] => Array
                (
                    [success] => 
                    [error-codes] => Array
                        (
                            [0] => timeout-or-duplicate
                        )

                )

            [_error] => The NoCaptcha verification has failed.
            [var] => 
        )