code: function sendBroadcast (message_creative_id, custom_label_id) {
    return new Promise (async (resolve, reject) => {
      if (!message_creative_id) {
        reject('Valid message_creative_id required');      
      }
  
      let options = {
        'message_creative_id': message_creative_id
      };    
  
      if (custom_label_id) options.custom_label_id = custom_label_id;
      
      try {
        let response = await this.callBroadcastApi(options);
        resolve(response);
      } catch (e) {
        reject(e);
      }    
    });
  }
docs: Sends a new broadcast message via the [Broadcast API](https://developers.facebook.com/docs/messenger-platform/reference/broadcast-api).
  @param  {Integer}  message_creative_id  The ID of a message creative to send in the broadcast. Created by calling {@link #createmessagecreative|Client.createMessageCreative()}.
  @param  {Integer}  custom_label_id   _Optional._ The ID of a custom label to target for the broadcast. Created by calling {@link #createcustomlabel|Client.createCustomLabel()}.
  @return {Promise}  The API response
  @memberof  Client#
  @example
  let message_creative_id = 499792492764246,
  custom_label_id = 097046973276-46; // optional
  Client.sendBroadcast(message_creative_id, custom_label_id)
  .then(res => {
  console.log(res); // {'broadcast_id': 397230957240952}
  });