Problem with language sitemap

Hi
I have installed Yoast on this site https://www.bulthaupmilano.it/ that use
https://www.ait-themes.club/wordpress-themes/hoteliour/
and
https://www.ait-themes.club/multilingual-support/

i think that href lang work fine and also the language selector to switch from
https://www.bulthaupmilano.it/ (italian default language)
and
https://www.bulthaupmilano.it/en/ (english)

but language sitemap https://www.bulthaupmilano.it/language-sitemap.xml
put https://www.bulthaupmilano.it/it/ (with it folder) that generate a 404 error and google alert me for href lang error.

i don’t know if is a theme error a language plugin error or yoast sitemap error.

regards
Francesco