Trying to create a Magento sitemap results in the error message “is not available and cannot be used”. This rather confusing message actually means that you need to call your sitemap sitemap.xml and not anything else! If you’re creating more than one sitemap e.g. when you have different stores, then you can create folders to put each of the sitemaps in e.g. create different folders in your Magento root directory for each additional store:
Then you can specify the filename sitemap.xml for each folder.