Hello,
Thank you for contacting Rank Math and bringing your concern to our attention. I’m sorry for any inconvenience this issue may have caused you.
For initial troubleshooting, ensure that the Robots meta of that post type is already set to index on your WordPress dashboard > Rank Math > Titles & Meta > [Post type] > Meta robots:

Also, please make sure that there is at least 1 post under that post type that is already indexed.
If the issue still persists, please follow the steps below:
1. Flush the Sitemap cache by following this video screencast:
https://i.rankmath.com/pipRDp
2. Exclude the Sitemap files of the Rank Math plugin in your caching plugin. The cache could be via a plugin or from the server. For plugins or Cloudflare, please follow this article: https://rankmath.com/kb/exclude-sitemaps-from-caching/
Hope that helps.
Thank you.
It worked 🙂
The sitemap slug was already set to be excluded in the cache plugin, but it seems that is not the cause. Curiously, I had to manually update it as you indicated to include the new posttype.
Hello,
We are super happy that this resolved your issue. If you have any other questions in the future, know that we are here to help you.
If you don’t mind me asking, could you please leave us a review (if you haven’t already) on https://wordpress.org/support/plugin/seo-by-rank-math/reviews/#new-post about your overall experience with Rank Math? We appreciate your time and patience.
If you do have another question in the future, please feel free to create a new forum topic, and it will be our pleasure to assist you again.
Thank you.