16023: Dial->Conference: Invalid participant label, must not exceed 128 characters, must not be a CallSid

The participantLabel attribute value specified in twiml on the conference noun was invalid. It may not exceed 128 characters, and it may not be a CallSid.

The twiml returned from an application or twiml bin contained a participantLabel value which is greater than 128 characters, or which resembles a CallSid ("CA" followed by 32 lowercase hexadecimal characters).

Shorten the value of the participantLabel attribute or avoid using a call SID.