Hi Aparna,
There is no way that your UI can get the CSRF token corresponding to the Gateway OData service . Remember that you have deployed your application in XS Engine. So, inside your XSJS context itself, make a GET call, and get your CSRF token corresponding to the OData which you are planning to POST to . Then make the post statement. (By the way, how did you get the gateway CSRF token in your UI ?)
Sreehari.