I think you and many others are looking at a beta marketing application called “ChatGPT” and you are trying to take this beta marketing application and program it like it was an API.
The API is called OpenAI API and requires a lot of programming to begin to “behave” like the ChatGPT web application.
Because of high demand for ChatGPT, OpenAI (and Microsoft) have already announced a ChatGPT API.
So, when the ChatGPT API arrives, programming ChatGPT-based applications will be a lot easier (we all think).
In the meantime, enjoy ChatCPT for “what is is” and not “what it is not”. ChatGPT is a beta marketing application to demonstrate the capabilities of OpenAI. ChatGPT is based on a large language model, it’s not a calculator. If you want to count words today, you should use the OpenAI API, because then you can easily count words when the completion returns.
Better, as mentioned, wait for the “coming very soon” ChatGPT API, and count those words when completions are returned, because for most people who love ChatGPT, it’s better to wait for the ChatGPT API to be released instead of getting frustrated that the OpenAI API is not ChatGPT 
Hope this helps.