I am getting this message that the theme is producing too much white space on updraft plus as well. https://www.velocitywebsites.co.nz/

Thank you for contacting the Yoast Support Team.
We understand you are having an issue with your XML Sitemaps:
error on line 6 at column 6: XML declaration allowed only at the start of the document
This typically happens when a plugin or theme function incorrectly adds an empty whitespace at the beginning of the sitemap. The Yoast SEO Premium plugin does not cause this issue.
However, the cause most often is an empty line at the end of the functions.php file. If there is no empty line in this file, we highly recommend running a conflict check to identify what outputs the empty white space. You may also need to clear your cache from your plugins/theme/CDN such as Cloudflare/server caching etc. If you are not sure how to clear caching please speak with your developers or contact your host provider.
Once you have identified whether your theme or a plugin causes the issue, please contact the developers of the theme or plugin for assistance finding and removing the whitespace.
I have cleared the cache. Any suggestions?