Move the calling function below the assignation:

$scope.GetLocatoinByCountry = function() {
  $http({
    method: 'POST',
    url: '/JobPost/GetLocationByCountry',
    data: {
      countryId: $scope.draftJobPost.countryID
    }
  }).then(function successCallback(response) {
    var loc = response.data;
    $scope.locations = response.data;
  }, function errorCallback(response) {
    var error = response;
  });
};

$scope.GetLocatoinByCountry(); // move it here

TypeError: $scope.GetLocatoinByCountry is not a function

The error says everything.

The issue was you were calling the function where it wasn't existed in the $scope and you were assigning the function to the $scope later on.

I think when using Angular 1 you can use $http or $resouce for calling API.

In your case: move the line $scope.GetLocatoinByCountry(); from above to below can make it work.