# E21xxx — Voice & SIP trunking

Error codes in the `E21xxx` range that the public Bird API returns. Each code links to its own page (the page its `doc_url` points at) with the cause and what to do. Retired codes stay listed; they are never renamed or reused.

| Code                                | Name                               | Status | Message                                                |
| ----------------------------------- | ---------------------------------- | ------ | ------------------------------------------------------ |
| [`E21006`](/docs/api/errors/E21006) | —                                  | —      | _Retired: no longer returned, never reused._           |
| [`E21008`](/docs/api/errors/E21008) | —                                  | —      | _Retired: no longer returned, never reused._           |
| [`E21048`](/docs/api/errors/E21048) | `VoiceInboundNumberAlreadyClaimed` | `409`  | Another SIP trunk already answers this inbound number. |

## Related

- [Errors](/docs/api/errors): the full wire contract, status mapping, and all code ranges
- [Error handling](/docs/guides/errors): branching on `type` and `code`, validation details, and `vendor_code`