Hello,
We apologize for the issue you are facing with the focus keyword on your page. It seems that Rank Math is indicating that the focus keyword you are trying to use has already been assigned to another post or page.
To resolve this, please ensure that the focus keyword is unique to each post or page. You can check if the keyword is being used elsewhere by navigating to your posts and categories in the WordPress dashboard. If you find that the keyword is indeed used on another page, you will need to either change it for the current page or modify the existing one.
If you continue to experience issues, we recommend replying to this ticket, and a human agent from the Rank Math Support team will assist you further. Thank you for bringing this concern to our attention!
Sources:
Why Can’t I Enter More Than 1 Focus Keyword in Post and Product Categories? » Rank Math
I checked several pages not showing targeted keyword in other pages. Need your support to fix the issue
Hello,
Thank you for contacting Rank Math support.
That SEO Test has a link that points to the actual post that uses the same keywords. You can click on the link and change the focus keyword to pass this test. Here’s a video:

We hope this helps clarify the issue. Please let us know if you have any other questions or concerns.
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.