Edit:
The actual reason for this error:
If an unauthorized user try to purchase an item then this message
should appear.
So if the App is not published, a non test user should get this error while try to purchase.
I realized that, Google play takes time to update the changes in app store. So you can not expect the changes immediately. Rather you should wait, in my case it took average 2/3 hours.
Still there may be some unknown error, which I could not figure.
My Cases:
First I was trying to purchase from my test device still got this error, But after waiting some time I didn't get this error. So I think the time was reason here.
Secondly I was trying from a non test device, which was an unauthorized device as the app was not published.