[Bug]: Error with OpenAI server: API request failed with status code 400

[boy-hack]

Your current environment

The output of `python collect_env.py`

🐛 Describe the bug

I encountered an error with the OpenAI server:

[openai_api_compatible] Error: API request failed with status code 400: {"object":"error","message":"{'type': 'string_type', 'loc': ('body', 'messages', 2, 'function_call'), 'msg': 'Input should be a valid string', 'input': {'name': 'function call', 'arguments': '{}'}, 'url': '[https://errors.pydantic.dev/2.6/v/string_type'}]","type":"BadRequestError","param":null,"code":400}

[boy-hack]

After thorough investigation of the code, I suspect the issue may lie in the formatting of the 'message'.

[hmellor]

Should be resolved by #3467