error on post_tag.xml

I have this error:
This page contains the following errors:

error on line 2 at column 1: Extra content at the end of the document
Below is a rendering of the page up to the first error.

this is page:
http://www.lebwindow.net/sitemap-tax-post_tag.xml

https://ww.wp.xz.cn/plugins/google-sitemap-generator/