I think you might want to correct ChatGPT to just GPT. As far as I know, there is no public API access point for the ChatGPT. OpenAI davinci model that you're likely using is based on InstructGPT ( a different GPT based beast ). Also, I would be somewhat worried about this thing racking up massive bills for the larger files.
EDIT: okay, according to replies there is more than meets the eye
EDIT: okay, according to replies there is more than meets the eye