angularjs - JWT authentication working with $http.get but not with $http.post

Question

I am new to MEAN stack. I am using jwt to authenticate api endpoint '/api/candidates'

In client-side/angular js service I have following entry

resumeFactory.get = function(candidateName) {
   return  $http.get('/api/candidates', {
      headers: {
        Authorization: 'Bearer '+ authenticationService.getToken()     
   });
};

on the server-side I have :

app.get('/api/candidates', auth, function (req, res) {
if (!req.payload._id) {
    //user not logged in
    console.log(req);
    res.status(401).json({"message": "no  user logged in from candidates"});
}
else {
    Candidate.find({}, function (err, candidates) {
        if (err) {
            res.send(err);
        }
        res.json(candidates);
    });
}
});

This works fine. i.e. 'auth' is able to extract the token from the header

When i change everything to post instead of get :

on client-side

$http.post()  

on server side :

app.post()

I get an error from jwt as following:

UnauthorizedError: No authorization token was found

Any suggestions on what is happening?. I can work with get but i want to know why post does not work