post 3 level json complex C# object to postasjsonasync

hi, 

i've a students class, which is of the form 

request format: 

students: [

{

"studentid" : "1234",

"researchid" : "5689",

"courses ": [{

 "courseName" : "os",

"professorName": "donchi lee"

},

{

"courseName" : "database",

"professorName": "jie, joe"

}]

"exams": [{

/*example data */

}]

}

]

lass foo { public List<StudentList> students { get; set; } }

class StudentList
{
     public string studentid { get; set; }

     public string researchId { get; set; }

     public List<courses> courseList { get; set; }
     public List<examsschedule> exams { get; set }
}

class courses {
    public string courseId { get; set; }
    public string courseName { get; set; }
    public string professsorName { get; set; }
}

class exams
{
    /****/
}

I

 have to post this as json to api. postasjsonasynch

When I send object of "foo" class, api rejects as it is not as json format.

var payload = fooObject/*object of foo*/var httpContent =newStringContent(payload,Encoding.UTF8,"application/json");
var httpresponse = httpclient.HttpClient.PostAsJsonAsync("url", httpcontent);
this returns either invalid format. if i use json serializer, it throws error as can not be serialized

I'm using web api's postasjsonaynch

[jsonproperty] is this used only for capturing response or also building request ?