# UNSUPPORTED_OBJECT_KEY

- Surface: API
- HTTP status: 400
- Details: `{ key: string, path: string[] }`

## Cause

A JSON own `"__proto__"` key reached a Zod record that would otherwise silently drop it (Precomputed Evaluations Flag Keys, or a shape that must keep every own key).

## Fix

Rename the key away from `"__proto__"`. `details.key` names the offending key and `details.path` is the wire path where it appeared. The platform refuses rather than returning a payload with that entry missing.

## Related

- [VALIDATION_ERROR](https://splitch.dev/docs/error/VALIDATION_ERROR)

Source: https://splitch.dev/docs/error/UNSUPPORTED_OBJECT_KEY