For the response_format you have to give it a whole json schema, which is a lot of work. It's just worth it for stuff like this, if you have the time for it. If you can't then that's probably not too bad either tbh, I've been using the Gemma 9B Instruct model with "Include no text aside from the JSON response. Do not wrap the JSON in quotes or markdown." added to the end of the prompt and it actually does it correctly 99% of the time.