Finally I resolved the issue of 401 Unauthorized.
I was getting 401 because my api_token was not granted with any permissions such as merchant, orders, etc.
I created new app in clover sandbox developer account. Though I was going to use only webapp but, I filled information related to android app also.
Steps followed :
1) Go to your clover sandbox developer account and click on Create New App.
2) Fill out Create New App and Quick Android App section.
3) Make sure you give required permissions in Permissions Section.
If you forgot to give the permissions at the time of app creation then you can change it later. Go to Developer Dashboard --> Your Apps --> Your App Settings --> Required Permissions
and give required permissions.
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