Thank you for contacting Rank Math, and sorry for any inconvenience caused.
The Discovered URLs 0 that you see in Google Search Console just means that the URLs in the sitemap were already found by Googlebot by other means, instead of via the sitemap. For example, Googlebot may have found the URLs from internal links or possibly from links on another site.
If you have submitted the sitemap recently, you need to wait for Google to crawl the sitemap.
Also, ensure that the sitemaps are excluded from caching:
Hope this helps.
Since we did not hear back from you for 15 days, we are assuming that you found the solution. We are closing this support ticket.
If you still need assistance or any other help, please feel free to open a new support ticket, and we will be more than happy to assist.