# 2026-09-26 — Request errors say what to fix (improvement · API, SDK, CLI · BREAKING)

> Every rejected request now returns a code and a message you can act on, schema failures list each invalid field, and malformed requests get their own codes.

A request that failed validation used to come back in the validator's own shape: `{ data, error, success }` on `/image/*` and `/video/*`, `{ success, errors }` elsewhere, with no `code` and your request echoed back. Now every request error has the same body:

```json
{
  "code": "VALIDATION_ERROR",
  "message": "model \"flux.2-pro\" is not supported. Did you mean \"black-forest-labs/flux.2-pro\"? See https://mynth.io/models, or GET /models, for the model IDs.",
  "issues": [{ "path": ["model"], "message": "model \"flux.2-pro\" is not supported. …" }]
}
```

`message` states every problem, so it is safe to show as it is. `issues` has one `{ path, message }` per field that failed the schema. An unknown model suggests the closest id, and an invalid `size` lists the forms it takes.

Two new codes cover requests that never reach validation:

- `INVALID_JSON` (`400`) for a body that is not valid JSON, with the parser's position. It used to be plain text.
- `UNSUPPORTED_MEDIA_TYPE` (`415`) for a JSON endpoint called without `Content-Type: application/json`, or `POST /image/upload` without `multipart/form-data`. Such a body used to be read as empty, so the error blamed a missing `prompt`.

A size a pinned model cannot produce, such as `16:9_4k` on a model without 4k, is now rejected at create with `400 VALIDATION_ERROR` and the size to use instead. It used to be accepted and then fail the task with `CAPABILITY_NOT_SUPPORTED`. With `model: "auto"` nothing changes.

Other messages got more specific too: input, resolution, duration, and audio errors list what the model accepts, `UNAUTHORIZED` says what is wrong with the credential, balance and spending-limit errors state the amounts, upload errors name the file, and a `404` names the route.

If your code reads `error`, `errors`, or `data` from a `400`, read `code`, `message`, and `issues` instead. `MynthAPIError` in the SDK now carries `issues` and a useful `message`, and the CLI exits with `2` for both new codes. See [errors](/docs/api-reference/errors#validation-errors).

Permalink: https://mynth.io/changelog/2026-09-26-clearer-request-errors · Markdown: https://mynth.io/changelog/2026-09-26-clearer-request-errors.md