Box AI with API returning blank response

I’m running a fairly straight-forward “ask ai question” API call, but it seems to be failing silently and returning a blank.  Using the same agent and prompt on box.com in UI on the same file, I get an answer, but when I call the exact same thing via API I get a blank.  I’m using the older boxsdk in python.  This is what my code looks like: 

    items = [
        {
            "id": file_id,
            "type": "file",
            "content": "This is the document in PDF format"
        }
    ]

    ai_agent = {
        'id':'40266263',
        'type': 'ai_agent_id'
    }

    result = client.send_ai_question(
            items=items,
            prompt=prompt,
            mode="single_item_qa",
            ai_agent=ai_agent
        )

 And I get this response:

{'answer': '[]', 'created_at': '2025-09-12T08:47:04.178-07:00', 'completion_reason': 'done', 'ai_agent_info': {'models': [{'name': 'openai__gpt_5', 'provider': 'openai'}], 'processor': 'basic_text'}}

I’m not sure what the issue is, I don’t get any errors, using the same agent and prompt in the UI gives the response I’m expecting.  Any help would be appreciated in how to troubleshoot this.