Hi Amit,
I am having the same issue with a webapp, however I am using the same build (v7.0 8935) for both the server and the client.
I have tried setting the user to the webAgent, an Admin or making the app anonymous access all without success.
Can you advise?
The only difference is that I am on a different network - could the campaign classic instance be whitelisting only certain IP ranges for access to the webapp preview? If so, how do I change this?
Thanks