How to integrate Transaction API in Action on Google

Question

Trying to integrate Transactions API for reservations only (No Payments required). While invoking transaction decision, the app is not responding and I hear “ is not responding right now. Try again soon.”

Here are my steps:
1. Check if transaction is required using transaction check
2. Create order, cart and transaction config.
3. Invoke transaction decision What am I doing wrong?

Here is the code, I want to keep my order with minimal information:

const order = assistant.buildOrder(`${new Date().getTime()}`)
    .setCart(assistant.buildCart().setMerchant('My Appointment', 'Appointment Project'));

const transactionConfig = {
    deliveryAddressRequired: false,
    type: assistant.Transactions.PaymentType.UNSPECIFIED,
    displayName: 'Book my appointment'
};

assistant.askForTransactionDecision(order, transactionConfig); // FAILS HERE

** assistant is app for dialogflow object

I have used the sample order from the GIT repo and documentation as well with Sandbox mode enabled and disabled, but it is still not working.

Testing on Nexus 5, Android Marshmallow, Fake Location of US and Dialogflow NodeJS client