> ## Documentation Index
> Fetch the complete documentation index at: https://developers.fireblocks.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Attach or detach labels to/from UTXOs

> Attach or detach labels to/from UTXOs in a vault account. Labels can be
used for organizing and filtering UTXOs.

Labels are applied additively — `labelsToAttach` adds to the existing
label set and `labelsToDetach` removes from it. Neither operation
replaces the full set.

The request is all-or-nothing: if any identifier cannot be labelled, no
UTXO is labelled and the request fails with `400`. The response lists
every failed identifier in `failures`, each with its own `reason` — use
it, not the status, to decide what to do:
- `NOT_FOUND` — not found in this vault and asset.
- `NOT_LABELLABLE` — spent, or removed, and can no longer be labelled.

A UTXO removed within the last hour is reported as `NOT_FOUND` with
`utxoStatus: REMOVED`; if it does not reappear, it becomes
`NOT_LABELLABLE` after about an hour. A `400` without `failures` means
the request itself is malformed.

Endpoint Permission: Admin, Non-Signing Admin, Signer, Approver,
Editor.



## API Specification

The full API specification for this endpoint is available in the [documentation index](https://developers.fireblocks.com/llms.txt).