Hi Rajeev, as I am passing authentication header with user credentials, I am not challenged to provide uid and password in pop up.
If I do not pass the header, I am prompted with the pop up. On entering the details, the pop is shown again . As if the entered details are incorrect.
I have tried this from Firefox n chrome. Both using rest client and pasting the GET URL in address bar.
I have tested both indepedent rest clients (soapui/cocarestclient) with pegaapi, it works for both 7.1.9 and 7.2.1. If you use the suggestion from Paraneeth, when you click 'try it out', you will be presented with browser popup to enter user/password, once you do that, it should be fine, see my screenshot: