Modify map content quantity and URL address

I need to customize how to adjust the links of the sitemap: This is because my site’s front-end and back-end are not under the same domain, so I need this feature.
In addition, it is necessary to split the number of site maps. I used the hook in the document to modify the generated quantity,
add_filter(‘seopress_sitemaps_max_posts_per_sitemap’, ‘sp_sitemaps_max_posts_per_sitemap’);
function sp_sitemaps_max_posts_per_sitemap() {
//default: 1000
return 100;
}
But it hasn’t even taken effect, how can I solve this problem?

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