# E04060 — ContactMatchKeyMissing

This entry does not carry the identifier the batch's match_on requires.

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

## What to do

Every entry in a batch that sets match_on must carry that field. Add it to this entry, or drop match_on to let each entry match on whatever identifiers it carries.

## 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`