# Set an activity deadline

`POST /v1/activities/:id/deadline` calls `crm.timeline.activity.setDeadline`.

```json
{"deadline":"2026-10-01T12:00:00Z"}
```

Success: HTTP 200 with the read-back activity in `data`. The service checks the deadline after the call: if Bitrix24 reports success without changing it, the response is 422 `ACTIVITY_DEADLINE_UNCHANGED`.