Create a webservice.lk account if you do not have one yet by simply clicking on Sign Up
Go to https://console.actions.google.com/
Name the project. Eg:- WebserviceLK. It Takes few seconds to create the project.
Now you are on the home screen. Click Home Control. Click Name your Smart Home Action.
Name it WebserviceLK. Click Save (in the upper right corner).
Click "Account Linking". Then Select No.
Select OAuth, then Select Autherization Code.
Now Copy Client ID and Client Secret from WebserviceLK website you have already created.
Paste it accordingly and click next.
Authorization URL: https://iot.webservice.lk/oauth
Token URL: https://iot.webservice.lk/token
Now Enter user (Just "user"). Click next.
Enter test. Click Save.
Now, Select Actions under Build from left side menu. Click Add your first action.
and Click Done. Then Click Test. This will deploy the thing and now you are ready to start testing.
Now you need to get control of your devices through Google Asistance by talking to it. So, add few devices in to your webservice.lk account by visiting it.
Open your Google Home mobile app in your android phone. (If you do not have it you must install it.)
Go to Home. (Or you can go to Settings)
Find Home Control in Left side panel.
Now you must see WebserviceLK (Or whatever name you have given, when creating it). Click on it. Now it will open a login page to login. Use your webservice.lk credentials to log in. Now you will see a message with link successful.
Now you will see your devices you have created in your webservice.lk account.
You have successfully done the application setup.