Sitemap for one website in multiple domains

I have 2 domains (A and B). The first one (A) is the website.

In sitemap.xml of “A” domain, I have a sub-sitemap in “B” domain with “A” URLs.

I have follow the documentation (https://support.google.com/webmasters/answer/75712?hl=en). So these 2 domains are verified in the Google Search Console but Google does not index the sub-sitemap (in “B” domain with “A” URLs). Other sub-sitemap in “A” domain are OK.

FYI: the sitemap is valid because if I send it manually in the Search Console (on the B domain property), URLs is displayed in Google search results. An for multiple reasons, I can’t sent it manually every time.

Do you have an idea ? Thanks