Following are the simple steps which can help you to get your client_secret.json file to setup synchronization with google calendar.
You need to create a Project in Google Developer Console. Click here
to go to Console page. It will ask you to login with your Google Account if you are not logged in already. If you have created Projects in Google Developers Console before you will see list of already created projects. If not, below screen will appear.
Start – Create Project in Google Developers Console
In both scenarios, Click on ‘Create Project’ button.
A popup will appear, where you will enter ‘Project Name’ and ‘Project ID’ which will help you to recognize your project in console.
Enter Project Name – Google Developers Console
By clicking on Create button, Your project will be created and redirects you to your projects list in Console.
Clicking on the project name which you have recently created will take you to your Project Dashboard.
See left side navigation menu. Go to APIs & auth -> APIs and Select ‘Calendar API’ and Turn in ‘ON’.
Enable Calendar API in Google Developers Console
Go to APIs & auth -> Credentials. Click on OAuth 2.0 Client ID
Change https://www.youwebsiteurl.com to your website's URL. Please NOTE it's very important to use right http in url. If your website is not using https then use http instead.
Download client_secret file and rename it to client_secret.json and upload it to libraries/google folder.
Visit your website URL with index.php?option=com_modern_booking&task=verifier
Example url www.mywebsite.com/index.php?option=com_modern_booking&task=verifier