422 — Unprocessable Entity — body shape is wrong

The request parsed as JSON but failed validation. The response body names the offending field.

Start free HTTP / REST → canonical

Diagnosis

When you hit this

Calling predict_breach with machine_id and threshold but no time_series. The endpoint is stateless and never reads stored telemetry, so the series is required every call.
A time series shorter than 16 points.
A canonical_field that is not in the schema.

Resolution

How to fix it

Send the series every time
Include time_series with at least 16 points, oldest to newest.
Validate the canonical field name
Query the coverage endpoint to confirm the field exists before sending it.
Read the error body
It names the failing field rather than just rejecting the request.

Normalization

What Forge does about it

The statelessness is the thing to internalize: prediction endpoints do not fetch history for you. Supplying {machine_id, field, threshold} and expecting Forge to look up the series is the single most common 422.