• command (string, required) Identifies the type of playback event. Enum: textPlaybackStart, textPlaybackStop, textPlaybackCancel

• batchSequence (integer, required) Auto-incrementing sequence number that identifies the TTS batch this event relates to.

The sequence starts at 0 for the first batch sent after the session is accepted and increments by 1 for each subsequent batch. Use this value to correlate playback events with the textResponse messages sent from the server.