Not stopping webform from submitting

We have added htcaptcha to a webform. Submitting the webform without ticking the captcha box is not stopping the form from submitting. `hcaptcha_captcha_validation` is run but is returning FALSE here

if (!isset($_POST['h-captcha-response']) || empty($_POST['h-captcha-response']) || empty($hcaptcha_secret_key)) {
    return false;
}

because `h-captcha-response` is empty.

I dont know enough about how hcaptcha works to know if that check is required or not.