Hi
current generation of sitemap.xml does not generate the categories urls. Only top level category links present in sitemap.xml
no error found so far from generating sitemap.xml manually via admin interface.

https://kleinanzeigen.ch/sitemap.xml

@MPM
Only category that contains at least 1 listing will be included in sitemap.

Hi,
The SEO plugin is of course not indexing empty categories but in fact it should. Please note that a new website made in OSCLASS need a lot of time to fill all the categories. Majority of these sites are in fact running by back filling empty categories from other sources or by google ads and it is very important to index the blank categories, regions, countries etc to monetize the site. Hope the developer consider this as an option for the new version of this  plugin and provide a button so if someone need the feature just turn it on and if someone don't want empty categories to be indexed he / she can turn the feature off.

thanks 

@Mohammad
It is called SEO plugin because it should help you to setup your site in way SEO likes it.
Your request is absolutely irrelevant, sitemap file is created for bots and I believe that bot is not so stupid that will not recognize that source code for 200 of your categories is same in 99%.

What would be benefit of that?