when you enter the correct api key, the inscription "invalid key" still pops up
It's strange, I tested and the api key seem to be working.
It's possible that the ChatGPT service might not work for a short period, could the issue be from there? Trying again now might solve it (or unfortunately, the service might still not be working).
Otherwise, when you entered the OpenAI/ChatGPT key, was it in this format? Did you press Enter after entering the key?
In case, there's a demo mode (extremely limited) that allows you to test the game.