OptionalEventOptional event-webhook URL for lifecycle events. Maps to Vonage's event_url.
Originating caller-id / DID. Maps to Vonage's from: { type: 'phone', number }.
The NCCO executed when the call connects (our connect websocket action). Maps to ncco.
Destination number (E.164). Maps to Vonage's to: [{ type: 'phone', number }].
The REST payload IVonageVoiceLike.CreateCall accepts (the subset we use).