Sitemap error: XML or text declaration not at start of entity
Are you seeing one of the following sitemap errors?
XML or text declaration not at start of entity
XML declaration allowed only at the start of the document
In this article, we provide you with steps you can follow to solve these errors.
Cause
This issue typically happens when a plugin or theme function incorrectly adds empty whitespace at the beginning of the sitemap. Please view the source code of your sitemap.

Solution
The cause most often is an empty line at the beginning (before the <?php
line) or end of the wp-config.php or functions.php file. If there is no empty line in these files, we highly recommend running a conflict check to identify what outputs the empty whitespace. Yoast SEO does not cause this issue.
You may also need to clear your cache from your plugins, theme and CDN such as Cloudflare or server caching. If you are not sure how to clear cache, 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.