# E04056 — ContactIdentifierRequired

A contact needs at least one reachable identifier. Supply an email address, a phone number, or both.

- **HTTP status**: `422`
- **Type**: `validation_error`
- **Name**: `ContactIdentifierRequired`

## What to do

Add an email address or a phone number. An external_id alone does not make a contact reachable.

## Related

- [E04xxx — Email sending & delivery](/docs/api/errors/E04xxx): every code in this range
- [Errors](/docs/api/errors): the full wire contract, status mapping, and error catalog
- [Error handling](/docs/guides/errors): branching on `type` and `code`, validation details, and `vendor_code`