# E21036 — VoiceCallerIDVerificationInProgressElsewhere

Another verification for this phone number is already in progress.

- **HTTP status**: `409`
- **Type**: `conflict_error`
- **Name**: `VoiceCallerIDVerificationInProgressElsewhere`

## What to do

A number can have only one verification in progress at a time. See https://bird.com/en-us/docs/guides/voice/caller-ids#one-verification-at-a-time for how caller ID verification works.

## Related

- [Idempotency](/docs/api/idempotency): safe retries and key reuse rules
- [E21xxx — Voice & SIP trunking](/docs/api/errors/E21xxx): 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`

## Related resources

- [Should I use a Bird SDK or call the API directly?](/explained/platform/should-i-use-an-sdk-or-call-the-api-directly) (answer)
- [Build your first integration](/learn/paths/integration) (course)
- [Send your first email](/docs/get-started/send-your-first-email) (docs)

[Get an implementation brief](/learn/workspace?topic=api-basics)