RealtimeServerEventInputAudioBufferDtmfEventReceived
SIP Only: Returned when an DTMF event is received. A DTMF event is a message that
represents a telephone keypad press (0–9, *, #, A–D). The event property
is the keypad that the user press. The received_at is the UTC Unix Timestamp
that the server received the event.
{
"type": "input_audio_buffer.dtmf_event_received",
"event": "string",
"received_at": 0
}