Hello,
Thank you for contacting Rank Math.
The option to assign a credit is only available in the Business and Agency License.
https://rankmath.com/kb/how-to-use-content-ai/#assign-content-ai-credits
With the Free account and PRO license, the credits can be used across all the connected websites.
Please head over to WordPress dashboard > Rank Math dashboard > Help > Disconnect and Connect again with your Rank Math account.
Then, head over to Content AI and refresh the credits count so the plugin will request the updated credits from our server:

Hope that helps. Please don’t hesitate to let us know if you need our assistance with anything else.
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.