# 16023: Conference: Participant label invalid (max 128 chars, not CallSid, no '/')

Log Type: APPLICATION

Log Level: ERROR

## Description

This error occurs when the `participantLabel` used to add a caller to a conference is invalid. For 16023, the label cannot be longer than 128 characters, cannot look like a Call SID, and cannot contain `/`, including `%2F`. You can use `participantLabel` later to reference a participant through conference participant operations.

### Possible causes

* The `participantLabel` value is longer than 128 characters.
* The `participantLabel` matches the Call SID pattern, which starts with `CA` and is followed by 32 lowercase hexadecimal characters.
* The `participantLabel` contains `/`.
* The `participantLabel` contains `%2F`, which decodes to `/`.

### Possible solutions

* Keep `participantLabel` at 128 characters or fewer.
* Use an application-defined label that does not look like a Call SID.
* Remove `/` and encoded slash values such as `%2F` before you send the label in TwiML or in a request that creates a conference participant.
* Store a stable label that your application controls, such as an internal user identifier or descriptive name, if you plan to fetch or update the participant later.

#### Additional resources

* [TwiML Voice: `<Conference>`](/docs/voice/twiml/conference)
* [Voice Conference](/docs/voice/conference)
* [How to Share Information Between Your Applications](/docs/voice/how-share-information-between-your-applications)