OpenAI has recently been allowing accounts to run into negative credits for a long time after $0.00 before being shut off. The hard limit also seems non-functional.
So if you want to see that your code will return an error when receiving that error, even though YOU don’t when the API should, you might need to make a new account without funds.
And don’t count on the API function to stop the account from going -$1000.00, as has been reported.
Then you can look into possible solutions for this specific case.
In the OpenAI cookbook is also an example to provoke and resolve a 429 error.
Please make sure you aren’t spending all your credits on debugging.