> ## Documentation Index
> Fetch the complete documentation index at: https://docs.bridgelinepf.com/llms.txt
> Use this file to discover all available pages before exploring further.

# INVALID_API_VERSION

> The `Bridgeline-Version` header isn't a real date in `YYYY-MM-DD` form.

`400 Bad Request` · type `invalid_request`

**When it happens**

You sent a `Bridgeline-Version` header that isn't a valid calendar date, such as `2026-9-23`, `v1` or `2026-02-30`.

**What to do**

Send `Bridgeline-Version: 2026-09-23`, or leave the header out to use the current version. See [versioning](/changelog#versioning).

## Example

```json 400 Bad Request theme={null}
{
  "error": {
    "type": "invalid_request",
    "code": "INVALID_API_VERSION",
    "message": "Bridgeline-Version must be a date like 2026-09-23.",
    "param": "Bridgeline-Version",
    "doc_url": "https://docs.bridgelinepf.com/errors#INVALID_API_VERSION",
    "request_id": "req_8fJ2kQ9xLm4TzW7nB3cY5pDv"
  }
}
```

See all [error codes](/errors), or how to [handle errors](/guides/errors).


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