16002: Failed to validate conference attributes

This error occurs when Twilio cannot validate one or more <Conference> attributes on a Voice conference. Check the attribute values, URL formats, and limits against the supported <Conference> options.

• statusCallbackEvent includes a value outside start, end, join, leave, mute, hold, modify, speaker, or announcement.
• recordingStatusCallbackEvent includes a value outside in-progress, completed, or absent.
• One or more URL attributes, such as waitUrl, statusCallback, recordingStatusCallback, or eventCallbackUrl, is missing or is not a relative or absolute URL.
• A method attribute uses a value other than GET or POST.
• maxParticipants is greater than 250, participantLabel is longer than 128 characters or is not unique, or coach is not a Call SID for a call already connected to the conference.

• Update each <Conference> attribute to use only supported values and formats. Use boolean values where required, use the documented event names, and keep maxParticipants at 250 or below.
• Provide valid relative or absolute URLs for waitUrl, statusCallback, recordingStatusCallback, and eventCallbackUrl, and use GET or POST for waitMethod, statusCallbackMethod, and recordingStatusCallbackMethod.
• Keep participantLabel unique and within 128 characters. If you use coach, set it to a Call SID that is already active in the conference.
• Prefer recordingStatusCallback over eventCallbackUrl, because eventCallbackUrl is deprecated and Twilio does not send eventCallbackUrl requests when recordingStatusCallback is provided.

• TwiML Voice: <Conference>
• Voice Conference