401 base.unauthorized error

I installed apache answer in my localhost, i tried posting the questions using the API (http://127.0.0.1:80/answer/api/v1/question), but then I am getting the 401 base unauthorized error. can somebody tell why?

{
    "code": 401,
    "reason": "base.unauthorized_error",
    "msg": "Unauthorized.",
    "data": null
}