# The write class cannot be asserted

`https://epcis.dev/errors/write-class-refused`

| | |
|---|---|
| status | 400 |
| retryable | false |
| costed | false |
| served by | epcis.dev |

A capture payload named a `spine:writeClass` the caller may not set. The class lattice is MONOTONE DOWNWARD: `simulated` is a self-downgrade and is accepted from anyone, because it can only shrink what an event is admissible for. `witnessed` is the gateway's DEFAULT and is stamped, never accepted — a class a request can claim is not a class, and the day a tenant is pinned simulation-only an accepted assertion would be an escape hatch that had always worked and therefore looked correct. Any other value fails closed.

## What to do

Omit `spine:writeClass` for the normal case — the gateway stamps `witnessed`. Declare `"simulated"` when the event is generated rather than observed. A tenant that must never emit witnessed events is pinned at its key, not at its payload.

## Derived from

- docs/specs/shared-surface.md §2.4
- docs/specs/verbs/epcis.dev.md §A5
- #195