Append custom sitemap to sitemap index I have a custom generated sitemap which I'd like to append to my SEOmatic sitemap.xml file.

Is this possible?

I suppose the simple alternative would be to just add an extra sitemap to Google Search Console?
This is actually pretty simple...

If you navigate to SEOmatic → Site Settings → Miscellaneous, you'll see a table at the bottom of the page where you can input custom sitemap urls.



Once you add a url in here and save it, it will get added to a custom index sitemap that is included at the bottom of your main index sitemap:

/sitemaps/1/sitemap.xml

&lt;sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"&gt;
  ...
  &lt;sitemap&gt;
    &lt;loc&gt; http://site.test/sitemaps/1/global/custom/1/sitemap.xml &lt;/loc&gt;
    &lt;lastmod&gt; 2018-11-16T10:06:31-05:00 &lt;/lastmod&gt;
  &lt;/sitemap&gt;
&lt;/sitemapindex&gt;


/sitemaps/1/global/custom/1/sitemap.xml

&lt;urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"&gt;
  &lt;url&gt;
    &lt;loc&gt; http://site.test/custom.xml &lt;/loc&gt;
    &lt;lastmod&gt; 2018-12-07T14:26:25-05:00 &lt;/lastmod&gt;
    &lt;changefreq&gt; weekly &lt;/changefreq&gt;
    &lt;priority&gt; 0.5 &lt;/priority&gt;
  &lt;/url&gt;
&lt;/urlset&gt;


for more info → https://github.com/nystudio107/craft-seomatic#additional-sitemap-urls