Model 'gpt-4o (or other model name)' not found

This means that your account (your API key) does not have the permission to use the model with your current tier level. If you are wondering why because you have the ChatGPT subscription, please refer to 'I have ChatGPT Plus subscription. Why can't I use OpenAI's paid models?' section in FAQ.

Solution

Add a Payment Plan: To access the latest models, you need to add a payment plan and purchase credits. You can do this by visiting the Billing Overview page.

Make a Payment: Ensure you make a successful payment (minimum $5). After the payment is processed, access to the latest models and higher rate limits should be enabled.