16001: Cannot Whisper Participant Until Conference Is Bridged

The call SID specified by the whisper parameter is invalid. This may because the specified call is no longer connected to the conference. Validate that this call is connecting to the correct conference and the call SID specified is also in the conference.

The conference participant that you are attempting to whisper is part of a conference that has not yet bridged. Please retry once a second participant has joined and the conference has bridged.