Change the name in the response – Not working?

I put this code snippet from your FAQ into the functions.php file, but is has no effekt. Where exactly should the value of ‘display_name’ appear in the mail response that the person who wote the response receives?

/**
 * @param string $responseBy
 * @param \GeminiLabs\SiteReviews\Review $review
 * @return string
 */
add_filter('site-reviews/review/build/tag/response/by', function ($responseBy, $review) {
    // Option 1:
    // The user ID of the person who wote the response is stored to the review,
    // so you can get their name like this:
    if ($user = get_userdata($review->meta()->_response_by)) {
        $responseBy = $user->display_name;
    }
    return $responseBy;
}, 10, 2);