# PRECONDITION_REQUIRED: Precondition required

> Updating or deleting an entry, type, trait, or asset, and replacing an asset's file, must say which version it changes, so that one person's write never silently overwrites another's.

Sent by the management API (428). The page: https://coho-cms.com/errors/precondition-required/

## What to do

Read the resource, and send its `ETag` in an `If-Match` header with the write.

## The response

```json
{
  "code": "PRECONDITION_REQUIRED",
  "type": "https://coho-cms.com/errors/precondition-required",
  "title": "Precondition required",
  "status": 428,
  "detail": "What went wrong in this request, in a sentence.",
  "instance": "/v1/projects/…"
}
```

Every error code: https://coho-cms.com/errors/