OPENAI_API_KEY environment variable must be set

[dapuzz]

Please add in documentation that a valid API key is needed even if you are using by default model 3.5

[fo02667]

please note that's not enough: you have to add a billing plan/payment method (at least credit card data) even for free plan otherwise you'll get the following error:
Error code: 429 - {'error': {'message': 'You exceeded your current quota, please check your plan and billing details. For more information on this error, read the docs: https://platform.openai.com/docs/guides/error-codes/api-errors.', 'type': 'insufficient_quota', 'param': None, 'code': 'insufficient_quota'}}