If you want to use ChatBot then use Sonnet-4.5 pretending to be ChatGPT If you follow Jeffs Advice, that is what should work with it. Even though you have your own API key for Gemini I expect Gemini might not work with with ChatBot. I use the ChatBot with Sonnet-4.5 and it works fine. 
I use the default and ChatBot works great:
MIT provides a generous amount of tokens so I can do most of what I want. 
For anything other than ChatBot 's default, I would use the advice here in Gordon's tutorial. If you go that way you will need your own api key.
Make sure you have credits for your tokens for other than free use.