function render_living_mandala() {
    return '<iframe src="https://yourdomain.com/living-mandala/index.html" width="100%" height="700" style="border:none;"></iframe>';
}
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/42/35/2033542/web/wp-content/plugins/living-mandala-shortcode/living-mandala-shortcode.php:1) in <b>/home/42/35/2033542/web/wp-includes/sitemaps/class-wp-sitemaps-renderer.php</b> on line <b>126</b><br />
<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="https://edgeofcreation.info/wp-sitemap-index.xsl" ?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"><sitemap><loc>https://edgeofcreation.info/wp-sitemap-posts-post-1.xml</loc></sitemap><sitemap><loc>https://edgeofcreation.info/wp-sitemap-posts-page-1.xml</loc></sitemap><sitemap><loc>https://edgeofcreation.info/wp-sitemap-taxonomies-category-1.xml</loc></sitemap><sitemap><loc>https://edgeofcreation.info/wp-sitemap-taxonomies-post_tag-1.xml</loc></sitemap><sitemap><loc>https://edgeofcreation.info/wp-sitemap-users-1.xml</loc></sitemap></sitemapindex>