Responses API Error 400 Bad request : Missing mutually exclusive parameters

[sridharvenkat]

Please read this first

• Have you read the docs?Agents SDK docs - Yes
• Have you searched for related issues? Others may have faced similar issues. - Yes

Describe the bug

The recent upgrade to 0.40. causing errors after function_tool_call processing.

Error code: 400 - {'error': {'message': "Missing mutually exclusive parameters: 'input[17].output[0]'. Ensure you are providing exactly one of: 'file_id' or 'image_url'.", 'type': 'invalid_request_error', 'param': 'input[17].output[0]', 'code': 'missing_mutually_exclusive_parameters'}}

Debug information

• Agents SDK version: 0.4.0
• Python version 3.12

Repro steps

We are noticing after the latest upgrade of SDK response api interactions are failing after some function tool calls.
Unsure if the below item in the session is causing issue

{
  "call_id": "call_z1rcE3rHla5uHQmpMwI2im2n",
  "output": [
    {
      "type": "input_image"
    }
  ],
  "type": "function_call_output"
}

Expected behavior

The SDK should not error after function call

[amirna2]

I ran into the same exact issue today after upgrading from 0.3.0 to 0.4.0. There appears to be a regression with tools structure output when they return a pydantic object. I got around the issue by remove the Session SQLite DB and starting fresh with 0.4.0..Obviously not something you want to do in production agents.

Tools in general have been a pain to deal with.

[ihower]

@sridharvenkat @amirna2 I looked into this issue and my best guess is that:

1. In one of your previous function calls, the output didn’t include image_url. You might have accidentally returned None, for example:

   @function_tool
   def fetch_image() -> ToolOutputImage | ToolOutputImageDict:
       return {
           "type": "image",
           "image_url": None,
       }

   When this gets sent to the OpenAI API, it triggers exactly the error you mentioned:

   openai.BadRequestError: Error code: 400 - {'error': {'message': "Missing mutually exclusive parameters: 'input[2].output[0]'. Ensure you are providing exactly one of: 'file_id' or 'image_url'.", 'type': 'invalid_request_error', 'param': 'input[2].output[0]', 'code': 'missing_mutually_exclusive_parameters'}}
   

2. The bigger issue is that the current SQLiteSession implementation ends up saving that problematic function output anyway. Once this happens, the conversation thread becomes permanently broken: every subsequent request will hit the same error, because that bad function call output will always sent back to the API.

A temporary workaround is to start a new thread (i.e., use a different SQLiteSession(session_id) ).

The proper fixes could be:

1. Make sure function tools never return an image_url of None.
2. Patch the SDK’s session mechanism: it shouldn’t persist items that cause API errors when a bad 400 response occurs.

[walsha2]

Just tacking on that I am seeing the "Missing mutually exclusive parameters" error as well in v0.4.0 and along with other odd errors like the following:

Error code: 400
{
  "error": {
    "message": "Invalid 'input[5].output[0].file_id': 'houRsa7pyDBJ3QGke8mM'. Expected an ID that begins with 'file'.",
    "type": "invalid_request_error",
    "param": "input[5].output[0].file_id",
    "code": "invalid_value"
  }
}

This is really weird because I am NOT USING the OpenAI files API. I just happen to have a tool call that is returning JSON in the form of:

{
 "file_id": "houRsa7pyDBJ3QGke8mM"
}

It almost seems like there is some sort of validation pollution or wire crossing happening with the outputs of user defined custom tool calls with the OpenAI native tools/APIs? Not sure, just a hunch, but I found this error very odd and surprising....

[sridharvenkat]

@ihower , I suspect its not the function call response causing this issue.

1. Our function calls don't return image its text only API response
2. We downgraded to 0.3.3 and things worked so its only in the latest SDK its failing
3. You are right, the biggest issue is, it corrupts the entire session, also we don't use SQLLiteSession. We have our own implementation using cosmos database.

[ihower]

@sridharvenkat @walsha2 This is a breaking change in version 0.4.0.

Before 0.4.0: The SDK always converted function outputs to strings automatically, no matter what type they were.
After 0.4.0: Function calling now supports images and files. Because of this, your output (i.e. dict) is treated as a file output, which causes your error.

Solution:

In your function's final return, convert your function output to a string explicitly: str({"file_id": "houRsa7pyDBJ3QGke8mM"})

[sridharvenkat]

Thanks @ihower ,

I couldn't relevant docs in 0.4.0 release logs. Do you mind helping me with that.
Our tool responses are pydantic models, Is the expectation now that they need to be serialized to string too?

[ihower]

@sridharvenkat Yes, if you want the same behavior as before, just add str() to your function return:

You can see str(result) in the old code:
https://github.com/openai/openai-agents-python/pull/1898/files#diff-5ac347b49c1353aa71dbf489f1d502cb26444e4b425d485aa5aed9ec40a1c054L826