16025: Dial->Conference: Participant label is in use by another participant

This error occurs when <Dial><Conference> sets participantLabel to a value that is already used by another active participant in the same conference. participantLabel must be unique across all participants in a conference. If Twilio detects a duplicate label, Twilio does not add the call to the conference and continues to the next TwiML verb.

• Your application assigned the same participantLabel to more than one inbound caller joining the same conference through <Dial><Conference>.
• Your application generated or reused a label that is already assigned to another active participant in that conference.
• The label is already in use by an active participant that was added to the conference through the Conference Participant API. participantLabel values must be unique across all participants in the conference, regardless of how each participant was added.

• Generate a participantLabel that uniquely identifies each participant in the conference.
• If you add participants through both <Conference> TwiML and the Conference Participant API, use one label naming strategy across both paths so the same value is not reused for another active participant.
• Review the active participants in the conference before you reuse a label. You can fetch, list, update, and delete active conference participants by label through the Participants subresource.
• Add fallback TwiML after <Dial><Conference> if you want the call to continue somewhere specific when Twilio rejects the duplicate label.

• TwiML Voice: <Conference>
• Conference Participant API
• Debugging Your Twilio Application