after successfully authenticated with api, i am getting error code CMN-102

Hello 

Need your help we are in production
according to dashboard => credentials section,
we have just changed sandbox credentials with production credentials  in above code and getting Invalid resource owner credentials.

output is 

{ "error" : "invalid_grant", "error_description" : "Invalid resource owner credentials", "errors" : [ { "errorCode" : "OAU-140", "message" : "Invalid resource owner credentials" } ] }
Uh oh, that did not work the way we expected.

What could be the reason for that or what should i need to change?

You would need to use the appKey and appSecret for the PROD Environment also, you would need to use the Production Credentials. 

Meanwhile, could you confirm if the server URL for PROD Environment is: https://platform.ringcentral.com