Hello,
Thank you for reaching out to us regarding the issue with Content AI not working on your website.
To resolve this, please ensure that you have refreshed the credits for Content AI. You can do this by navigating to WordPress Dashboard → Rank Math → General Settings → Content AI and refreshing the credits. Here’s a screenshot for reference:

After refreshing the credits, try using Content AI again, and it should work without any issues. If you encounter any further difficulties, please feel free to let us know so we can assist you accordingly.
We appreciate your patience and understanding.
Sources:
Content AI Overview » Rank Math
How to Bulk Generate SEO Meta Tags Using Content AI » Rank Math
How to Use the Content AI Tools in Rank Math SEO » 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.