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.
You may try looking for the error code on your WordPress Dashboard > Rank Math > Instant Indexing > IndexNow History > Response.
Let us know how this goes.
Thank you.
As I told you earlier the same indexnow history throws me that error.

Hello,
Thank you for providing additional details on the issue.
In this case, head over to Rank Math > Instant Indexing > IndexNow settings > API Key > Change key:
https://rankmath.com/kb/how-to-use-indexnow/#change-api-key
Then, clear your website’s cache and try submitting URLs.
Hope that helps.
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.