In order to connect to a Dialogflow bot you should create a service account for testing purposes. From the Google Cloud Platform sidebar, pick "IAM & Admin" and then Service Accounts.
After clicking on the button, pick your bot from the modal window and click "Open".
Click on the button, name appropriately your service account, and then click "Create".
In the second step, set the Role to Viewer (optionally) and click on Continue.
In the third step, click the button, and with JSON selected click on Create. Safekeep the downloaded JSON file to upload to our bot connector.
Dismiss the modal and click Done.