Hello,
Thank you for reaching out to us. We’re sorry to hear that you’re experiencing issues with Content AI.
We recently released a revamped version of Content AI, and you might need to refresh the credits to start using it. Please head over to WordPress Dashboard → Rank Math → General Settings → Content AI and refresh the credits. Here’s a screenshot for reference:

Once you’ve refreshed the credits, please try using Content AI again, and it should work without any issues.
If you encounter any further problems or need additional assistance, please don’t hesitate to let us know.
Sources:
Content AI Overview » Rank Math
How to Use Rank Math’s Content AI for SEO » Rank Math
Content AI – Your Personal AI Assistant by Rank Math
How to Become a Content Editor Power User » Rank Math
This is an automated reply from Rank Math Support Bot. If you need further assistance, please reply to this topic and a human support agent will reply to you shortly.
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.