wp-sitemap.xml not generated

Hello,

When I go to /sitemap.xml on my website, it redirects to wp-sitemap.xml, but instead of generating a sitemap, the main page of my site is loaded. When I debug the php code;

wp-includes/sitemaps/class-wp-sitemaps.php line 200:

$provider = $this->registry->get_provider( $sitemap );

if ( ! $provider ) {
return;
}

$sitemap = ‘wp’ and get_provider returns null. So sitemap not generating and my site’s homepage is loading.

When I go to /index-sitemap.xml instead of /wp-sitemap.xml, it works, but I am not sure if the page loaded here is a correct sitemap and I want to know why wp-sitemap.xml is not working.