I had the same. I think the installer did not include the Chatbook paclet installation.

I manually installed the paclet with:

PacletInstall["Wolfram/Chatbook"]

This solved the issue for me.

Out of curiosity, do you have a ChatGPT Plus subscription, but no (trial) OpenAI API key?

For the OpenAI Mathematica notebook features (including chat) to work you need an OpenAI API key. You can get a key to use the API in a trial for 3 months (with a max rate and max $5, but it can get you far enough).

The ChatGPT Plus subscription and the OpenAI API are billed separately. The ChatGPT Plus subscription covers usage exclusively on the chat.openai.com platform and costs $20 per month, providing benefits such as general access even during peak times, faster response times, and priority access to new features and improvements.

On the other hand, the OpenAI API has its own separate pricing structure. It allows developers to integrate the OpenAI models, including ChatGPT, into their own applications or software. The API usage is billed based on the number of API calls made and the amount of tokens processed. The API usage is not covered by the ChatGPT Plus subscription, and it requires a separate subscription and separate payment.

The chat-notebook works, but the error is an OpenAI error:

A rate limit error indicates that you have hit your assigned rate limit. This means that you have sent too many tokens or requests in a given period of time, and the OpenAI services have temporarily blocked you from sending more.

For now we are going to have to just call the Chat enabled notebook a failure

Since chat notebooks worked fine for you with the Wolfram supplied test API key and for many other users (including me), the problem is with the API key you are using and not chat notebooks. Have you tried accessing the API some other way, e.g. Python?

pip install openai

Then execute this Python code after replacing YOUR API KEY with your API key

import os
import openai
openai.api_key = "YOUR API KEY"

completion = openai.ChatCompletion.create(
  model="gpt-3.5-turbo",
  messages=[
    {"role": "user", "content": "What is ChatGPT."}
  ]
)

print(completion.choices[0].message.content)

If you start the Chat-Notebook for the first time, Mathematica should have shown you a separate window with a form to fill in your OpenAI API key. You need to do that again if you use LLMFunction for the first time.

If Mathematica did not show you the form, I assume you can try to re-install the (offending) paclet by uninstalling it first:

PacletUninstall["Wolfram/LLMFunctions"]'
PacletUninstall["Wolfram/Chatbook"]

My assumption seems to backed up here: https://mathematica.stackexchange.com/questions/285713/how-to-use-the-new-llmfunction/285714#285714

Thanks for the useful tips from this post, it allowed me to set up the API Key installation and start using the IA chat. However, I almost all the time face an error message "An unexpected error occurred. Failure Message: Unexpected response from OpenAI server with status code 400. Tag: Chatbook::UnknownStatusCode ] Then, I can't use the functionnality. Frustrating....

Dave, how can I enter my OpenAI API Key? I didn't find any description about it, nor is it mentioned in the Settings... of my Mathematica for MacOS. I have ChatGPT+ license and have my key available, of course.

Thanks Dave. I did what you suggested but now I get another error: