Sitemap_index.xml show the error

My website : filmybook.cf
Sitemap url : https://filmybook.cf/sitemap_index.xml
Sitemap_index.xml shows the following error:

This page contains the following errors:
error on line 1 at column 71: XML declaration allowed only at the start of the document
Below is a rendering of the page up to the first error.
window.oncontextmenu = function(){return false;}