Add page's relative URL to a GravityForms confirmation when using "page" type

gf_relative_url_page_confirmation.php

// GravityForms return relative URL from page-type confirmations
add_filter( 'gform_pre_confirmation_save', function ($confirmation, $form) {
    if ($confirmation['type'] === 'page') {
        $confirmation['url'] = get_page_uri($confirmation['pageId']);
    }

    return $confirmation;
}, 10, 2 );

Recently I had an issue where I was using GravityForms to power some forms on a Gatsby frontend. When the forms were submitted, I needed to go to the page set in the GF confirmation. In WordPress this is simple, you can get a page URL from its ID, which is all that was returned with a "Page" type confirmation. I needed the relative URL, as Gatsby can't convert the ID to a URL.

This will return the relative URL with any page-type confirmation. It will also pass that data through REST API, WPGraphQL, and into the Gatsby GravityForms source plugin.