Hello,
Thank you for contacting Rank Math and sorry for any inconvenience that might have been caused due to that.
Could you please share the specific URL you are having trouble with so that we can assist you accordingly?
Thank you
Hello,
I have checked the Sitemap of your website and I see that it is generated using Google Sitemap Generator Plugin. In this case, please make sure that you have disabled the Sitemap module of Rank Math in WordPress Dashboard > Rank Math > Dashboard.
I have tried to validate the Sitemap and there’s no issue detected.
Here is a screenshot for your reference:

Now, please check if you verified the correct version of your website on Bing. Please check if you have verified the www (or non-www) and HTTPS (or HTTP) versions of your website. If there is a mismatch, please fix that.
Finally, make sure you have cleared the cache and excluded the Bing bot from seeing a cached version of your sitemap.
If you have followed these, then the error must be coming from Bing. We suggest you please contact Bing Support for further assistance.
Thank you
Hello,
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.
Thank you.