# Revision conflict

_Wispist / Problems_

> HTTP 412 problem returned when a create-only ID exists or a replacement or deletion no longer matches the observed document revision.

Canonical type:

```text
https://learn.peios.org/wispist/problems/revision-conflict/
```

Status: `412 Precondition Failed`. Browser code: `revision_conflict`.

The mutation's HTTP precondition did not match current state:

- `If-None-Match: *` was used to create an ID that already exists.
- `If-Match` carried an older revision for replacement or deletion.

Fetch or wait for the latest document, reconcile the user's intent, then submit a new conditional mutation using that revision. Never loop blindly: another caller may have made a meaningful conflicting change.

The browser client's `replace`, `update`, and `delete` methods accept an observed document envelope so safe concurrency is the normal path.

Related content:

- [Problem Details](/wispist/problems/overview.md)
- [Documents and collections](/wispist/using-wispist/documents-and-collections.md)
- [Browser API reference](/wispist/reference/browser-api.md)