Simple Sitemaps for Multisite Plugin

There is some issues with the Multisite Sitemap plugin and every time i try and update i get the a parse error, debug is showing these errors?

Notice: wp_get_sites is deprecated since version 4.6.0! Use get_sites() instead. in /home/orbsitesco/public_html/wp-includes/functions.php on line 3706

Warning: Cannot modify header information - headers already sent by (output started at /home/orbsitesco/public_html/wp-includes/functions.php:3706) in /home/orbsitesco/public_html/wp-includes/pluggable.php on line 1174
Simple Sitemaps file "sitemap.php" not found. Please move it to /wp-content/ before activating.

Is anybody able to fix the plugin?