16024: Participant label invalid: max 128 chars, not a CallSid, no '/'

You receive this error when you send a POST request to create a Conference participant with an invalid Label. The value must be 128 characters or fewer, it cannot resemble a Call SID, and it cannot contain /, including %2F.

• Your request sets Label to a value longer than 128 characters.
• Your request uses a Call SID, or a value that resembles a Call SID, as the participant label.
• Your request includes / in the Label value.
• Your application URL-encodes / as %2F and sends it as part of the label. This is still invalid.

• Validate Label before you create the participant. Keep the value at 128 characters or fewer.
• Use a custom participant label instead of a Call SID. You can use that label later to fetch, update, or delete the participant.
• Remove / from your label generation logic. Do not rely on %2F as a workaround because Twilio rejects that value too.
• If you use labels in participant URLs later, percent-encode other non-URL-safe characters in the request path. For example, encode spaces as %20.

• Conferences Participants subresource
• Voice Conference
• Create Conference Calls