BerriAI/litellm · warning · HTTPException

Fixed margin amount for {provider} must be non-negative

Error message

Fixed margin amount for {provider} must be non-negative

What it means

Validation error (HTTP 400) from PATCH /config/cost_margin_config in the complex dict format: 'fixed_amount' is a number but negative. A margin surcharge cannot reduce cost, so LiteLLM requires fixed_amount >= 0 (0 is allowed, meaning no fixed component).

Source

Thrown at litellm/proxy/management_endpoints/cost_tracking_settings.py:395

                if not isinstance(percentage, (int, float)):
                    raise HTTPException(
                        status_code=400,
                        detail=f"Margin percentage for {provider} must be a number",
                    )
                if not (0 <= percentage <= 10):
                    raise HTTPException(
                        status_code=400,
                        detail=f"Margin percentage for {provider} must be between 0 and 10 (0% to 1000%)",
                    )
            if "fixed_amount" in margin_value:
                fixed_amount = margin_value["fixed_amount"]
                if not isinstance(fixed_amount, (int, float)):
                    raise HTTPException(
                        status_code=400,
                        detail=f"Fixed margin amount for {provider} must be a number",
                    )
                if fixed_amount < 0:
                    raise HTTPException(
                        status_code=400,
                        detail=f"Fixed margin amount for {provider} must be non-negative",
                    )
            if not margin_value:  # Empty dict
                raise HTTPException(
                    status_code=400,
                    detail=f"Margin config for {provider} cannot be empty. Must include 'percentage' and/or 'fixed_amount'",
                )
        else:
            raise HTTPException(
                status_code=400,
                detail=f"Margin for {provider} must be a number (percentage) or dict with 'percentage' and/or 'fixed_amount'",
            )

    try:
        # Load existing config
        config: Final = await proxy_config.get_config()

View on GitHub (pinned to 77b7c6c40c)

Solutions

Use a non-negative fixed_amount; remove the key or set 0 if not needed.
Model discounts with PATCH /config/cost_discount_config instead, which is the designed mechanism.
Validate the sign of computed markups in your config pipeline.

Example fix

# before
{"openai": {"fixed_amount": -0.001}}

# after
{"openai": {"fixed_amount": 0.001}}

Defensive patterns

Strategy: validation

Validate before calling

for provider, margin in cost_margin_config.items():
    if isinstance(margin, dict):
        fa = margin.get("fixed_amount")
        if fa is not None and fa < 0:
            raise ValueError(f"{provider}: fixed_amount must be >= 0; use cost_discount_config for discounts")

Prevention

Margins only add cost; use the discount config endpoint to reduce it.
Assert non-negative values for every monetary field in your schema.

When it happens

Trigger: Sending {"fixed_amount": -0.001} to try to model a discount; sign errors from spreadsheet exports or arithmetic that produced a negative surcharge.

Common situations: Trying to express provider discounts through the margin API instead of cost_discount_config; copy-paste sign mistakes.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

AI-assisted analysis of BerriAI/litellm@77b7c6c40c (2026-08-18). Data as JSON: /api/errors/61c19286c2126d0d. Report an issue: GitHub.