Hello,
Thank you for contacting Rank Math, and sorry for any inconvenience caused.
I logged in and checked the website settings.
The PRO plugin was not installed on your website, I have installed the plugin by following this guide:https://rankmath.com/kb/how-to-upgrade-to-rank-math-pro/

I also noticed that the Google XML Sitemaps plugin is active on your website, you should only use one plugin to generate the sitemaps.
Please deactivate the sitemaps plugin, or if you want to use that plugin for sitemap, disable the sitemap module in the Rank Math dashboard.
I hope this helps. Looking forward to helping you.
after removing xml site maps plugin the error still persists
Hello,
I’ve cleared the notification by clicking on the x button and then cleared the cache.
The issue is fixed.
Please check and let us know if you have any questions.
We are here to help you.
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.