> ## Documentation Index
> Fetch the complete documentation index at: https://wb-21fd5541-docs-1917.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# How do I fix an `anaconda 400 error` during a sweep?

The following error usually occurs when you do not log the metric that you are optimizing:

```
wandb: ERROR Error while calling W&B API: anaconda 400 error:
{"code": 400, "message": "TypeError: bad operand type for unary -: 'NoneType'"}
```

To fix this, make sure you are logging the exact metric specified in your sweep configuration. For example, if your sweep config specifies:

```yaml theme={null}
metric:
  name: validation_loss
  goal: minimize
```

Then your training code must call:

```python theme={null}
wandb.log({"validation_loss": value})
```

The metric name must match exactly between your sweep configuration and your `wandb.log` call.

For more information, see [Sweeps troubleshooting](/models/sweeps/troubleshoot-sweeps/) and [Define sweep configuration](/models/sweeps/define-sweep-configuration/).

***

<Badge stroke shape="pill" color="orange" size="md">[Sweeps](/support/models/tags/sweeps)</Badge><Badge stroke shape="pill" color="orange" size="md">[Metrics](/support/models/tags/metrics)</Badge>