Getting 'Token is invalid or has expired.' every time

Here is my code:

var KiteConnect = require("kiteconnect").KiteConnect;
var kc = new KiteConnect({ api_key: "xxxxxxxxxxxxxxxx" }); // (16 digit api_key)

........

    console.log("zerodhaLogin - start");
    console.log("request_token = ");
    console.log(request_token);

    if (request_token == null) {
      console.log("Invalid request token");
      cb("Invalid request token");
    }

kc.generateSession(request_token, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx")   // (32 digit app secret)
      .then(function (response) {
        console.log("KC::generateSession Response == ");
        console.log(response)
        init();
      })
      .catch(function (err) {
        console.log("Error in KC:generateSession : ERROR = ");   //// Always getting here with error 'Token is invalid or has expired'
        console.log(err);
        cb(null, err);
      }).finally(function (e) {
        // On finish
        console.log("KC:: --  finally: -- e == ");
        console.log(e)
      });

    function init() {
      // Fetch equity margins.
      // You can have other api calls here.

      kc.getMargins("equity")
        .then(function (response) {
          console.log("KC::Got Your margins: -- Response == ");
          console.log(response)
          // You got user's margin details.
          cb(null, "THANK YOU");

        }).catch(function (err) {
          // Something went wrong.
          console.log("KC:: --  ERROR in Getting Your margins: -- ERROR == ");
          console.log(err)
          cb(null, err);
        }).finally(function (e) {
          // On finish
          console.log("KC:: --  finally: -- e == ");
          console.log(e)
        });
    }

.......

I am getting correct request_token on my server but still 'generateSession' API call fails with error: 'Token is invalid or has expired'

Below is the output on console:

0|server | zerodhaLogin - start
0|server | request_token =
0|server | xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx // 32 digit request_token from redirect rest call
0|server | Error in KC:generateSession : ERROR =
0|server | { status: 'error',
0|server | message: 'Token is invalid or has expired.',
0|server | data: null,
0|server | error_type: 'TokenException' }
0|server | KC:: -- finally: -- e ==
0|server | undefined