[Bug]: Error while using allowed_openai_params with openrouter

[bgeneto]

What happened?

If you configure a Openrouter model with allowed_openai_params: ["user"] so you can track spent directly in openrouter dashboard the request fails with BadRequestError

  - model_name: gpt-5
    litellm_params:
      model: openrouter/openai/gpt-5-chat
      api_key: os.environ/OPENROUTER_API_KEY
      allowed_openai_params: ["user"]

I think it already worked before.

Relevant log output

litellm.BadRequestError: OpenrouterException - {"error":{"message":"Expected string, received null","code":400}

Are you a ML Ops Team?

No

What LiteLLM version are you on ?

v1.75.8

Twitter / LinkedIn details

No response