# X_ACTION_DEPRECATION_INVALID

## Means

an action declares a deprecation whose dates cannot be rendered

## Typical cause

a `deprecated: { since, sunset }` value that is not a date. Refused where the declaration is converted, so the route and the OpenAPI operation refuse the same value — a `Sunset` header rendering `Invalid Date` is a contract statement no client can act on

## Fix

edit `deprecated: { <field>: … }` on the action to an ISO-8601 instant — e.g. `'2026-12-31T23:59:59Z'`

[Actions](/error-codes#actions)