Hello,
Thank you for your query and we are so sorry about the trouble this must have caused.
We have replied to this ticket about the issue. But we are sending here our findings as well.
We don’t see any connected website in your account: https://rankmath.com/my-account/websites/
Please install or update your Rank Math Plugin to the latest version: https://rankmath.com/changelog/
You can disconnect your account by navigating to WordPress Dashboard > Rank Math > Dashboard > Help
and then simply disconnect the account by clicking on Disconnect Account.

Once you’ve disconnected your Rank Math account, you can connect it again in the same settings. In order to connect your correct account, click on Connect Now.

Once you click on Connect Now, please ensure that you’ve selected the correct account and then click on OK, Activate Now, as shown below.
Then head over to WordPress Dashboard → Rank Math → General Settings → Content AI and refresh the credits. Here’s a screenshot for reference:

Once done, please go back to using Content AI and it should work without any issues.
If the issue still persist after connecting the site, we might need to take a closer look at the settings. Please edit the first post on this ticket and include your WordPress & FTP logins in the designated Sensitive Data section.
Please do take a complete backup of your website before sharing the information with us.

It is completely secure and only our support staff has access to that section. If you want, you can use the below plugin to generate a temporary login URL to your website and share that with us instead:
https://wordpress.org/plugins/temporary-login-without-password/
You can use the above plugin in conjunction with the WP Security Audit Log to monitor what changes our staff might make on your website (if any):
https://wordpress.org/plugins/wp-security-audit-log/
We really look forward to helping you.