Hello,
Thanks for contacting the support.
We can check that your subscription status is already set as PRO:

Please follow this guide to install and activate Rank Math PRO on your site: https://rankmath.com/kb/rank-math-pro-license-key/
Hope this helps. Let us know if you need any other assistance.
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.