Hi @praful_patel,
Welcome to the community! 
All the information is very helpful upfront for gettings started with your issue, and is much appreciated.
However, I do not believe the issue you are seeing is related to the TLS ciphers. Rather, I feel it may have to do with cookies. Have you logged in on browser before? You may have a cookie there that establishes you a authenticated connection/session with the server.
Postman would likely not have that cookie if you have never established and authenticated connection/session with the server.
What is the 401 Error response body that you receive? That may also shed some more light on whats going on.
Additionally, how are you trying to authenticate with the server in Postman?
Regards,
Orest