Create unique Cred Frontend Editor url's after form submission so this can be tracked in Google Analytics. See https://wp-types.com/forums/topic/different-thank-you-pages-in-cred-depending-on-the-url-parameter/#post-263521, because you need to add more code to your CRED form!

functions.php

// Add parent page ID's to the thank you pages after form submission through CRED forms. More code needs to be added in CRED form itself, see https://gist.github.com/Willem-Siebe/a30f4ba5ff3607923ebc.

add_shortcode('wsis-sc-get-url-param', 'wsis_get_url_param');
function wsis_get_url_param ($atts) {
    $var = $atts["var"];
     
    return $_GET[$var];
}

function wsis_add_parent_page_id_to_redirect_page($url, $post_id, $form_data)
{
    $parent_page_id = $_POST["parent_page_id"];
 
    if(!empty($parent_page_id)) {
                  
        return $url .= '?parent_page_id='.$parent_page_id;
         
    }
     
    return $url;
}

add_filter('cred_success_redirect', 'wsis_add_parent_page_id_to_redirect_page',10,3);