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

# version_mismatch

> HTTP 400 — the X-API-Version header does not match the version in the path.

The API version is carried in the path prefix (`/v1/…`). The
`X-API-Version` header is optional, but when you send it, it must name the
same version — `1` or `v1` for a `/v1/` path.

**Not retryable.** Remove the header or make it agree with the path.

All error codes and the retry model: [Errors](/problems/overview).