Hello,
Thank you for reaching out to us. We’re sorry to hear that you’re having trouble accessing Content AI.
To access Content AI, please ensure that you have refreshed the credits. You can do this by heading over to WordPress Dashboard → Rank Math → General Settings → Content AI and refreshing the credits. Here’s a screenshot for reference:

Once you’ve done that, please try using Content AI again, and it should work without any issues.
If you need further assistance, please don’t hesitate to let us know.
Sources:
How to Use the Content AI Tools in Rank Math SEO » Rank Math
How to Connect/Disconnect Your Website From Content AI
How to Use Content AI in Block Editor » Rank Math
Hello,
We are glad to know that this issue has been resolved. Thank you for letting us know.
This ticket will be closed now, but you can always open a new one if you have any other questions or concerns. We are here to help you with anything related to Rank Math.
We appreciate your patience and cooperation throughout this process.
Thank you for choosing Rank Math.