node.js - DialogFlow V2 Webhook - Expects Speech responses Immediately and not after async requests

Question

I have a DialogFlow V2 node.js webhook.

I have an intent that is called with a webhook action:

const { WebhookClient } = require('dialogflow-fulfillment');
const app = new WebhookClient({request: req, response: res});

function exampleIntent(app) {

   app.add("Speak This Out on Google Home!");   // this speaks out fine. no error. 
}

Now, if I have an async request which finishes successfully, and I do app.add in the success block like this:

 function exampleIntent(app) {  
      myClient.someAsyncCall(function(result, err) {
          app.add("This will not be spoken out");  // no dice  :(
      }
      // app.add("but here it works... so it expects it immediately");
  }

... then Dialog Flow does not wait for the speech to be returned. I get the error in the Response object:

  "message": "Failed to parse Dialogflow response into AppResponse, exception thrown with message: Empty speech response",

How can I make DialogFlow V2 wait for the Webhook's Async operations to complete instead expecting a speech response immediately?

NOTE: This problem only started happening in V2. In V1, app.ask worked fine at the tail-end of async calls.

exampleIntent is being called by the main mapper of the application like this:

let actionMap = new Map();
actionMap.set("my V2 intent name", exampleIntent);
app.handleRequest(actionMap);

And my async request inside myClient.someAsyncCall is using Promises:

exports.someAsyncCall = function someAsyncCall(callback) {
    var apigClient = getAWSClient(); // uses aws-api-gateway-client
    apigClient.invokeApi(params, pathTemplate, method, additionalParams, body)
    .then(function(result){
        var result = result.data;
        var message = result['message'];
        console.log('SUCCESS: ' + message);
        callback(message, null);  // this succeeds and calls back fine. 
    }).catch( function(error){
        console.log('ERROR: ' + error);
        callback(error, null);
    });
};

Answer 1

Waitting for answers