Allowed Referrer Page

// Allowed Referrer Page / Kiri Vadivelu / 2026

add_action('template_redirect', function() {

    // ID of the page to protect eg. Thank You page

    if (!is_page(123)) {

        return;

    }

    // URL of the allowed referring page

    if (wp_get_referer() === 'https://yoursite.com/form-page/') {

        return;

    }

    // Redirect unauthorized direct access

    wp_redirect(get_home_url());

    exit;

});