Question

When I pass this request it pass null to request parameter on server site.
Is there any wrong with data attribute?

$.getJSON('http://127.0.0.1:81/api/sites/GetDomainAvailability?apikey=asfasfdsf&callback=?', { "request": '{"SubDomain":"asfsadf","ParentDomain":"asfasdf","ResellerId":"asfdsd"}' }, function (results) {

    alert('Cross domain JS call achieved. Have your implementation going in here!');
});

API C#

[HttpGet]
public HttpResponseMessage GetDomainAvailability(GetDomainAvailabilityRequest request)
{
    if (ModelState.IsValid)
    {
        if (request == null) return Request.CreateResponse(HttpStatusCode.BadRequest, "Invalid Request");
        var domain = string.Format("{0}.{1}", request.SubDomain, request.ParentDomain);

        var manager = new CloudSitesManager();
        var isDomainAvailable = manager.GetDomainAvailability(domain);

        HttpResponseMessage response = Request.CreateResponse(HttpStatusCode.OK, isDomainAvailable);
        return response;
    }
    else
    {
        return Request.CreateResponse(HttpStatusCode.BadRequest);
    }
}

[Serializable]
public class GetDomainAvailabilityRequest
{
    public string SubDomain { get; set; }
    public string ParentDomain { get; set; }
    public string ResellerId { get; set; }
}

Answer 1

It’s a problem with the model binding. Start with trying this:

$.getJSON('http://127.0.0.1:81/api/sites/GetDomainAvailability', {SubDomain:"asfsadf",ParentDomain:"asfasdf",ResellerId:"asfdsd"}, function (results) {

    alert('Cross domain JS call achieved. Have your implementation going in here!');
});

if this above doesn’t work, try this. I took this from some code I have doing the exact same thing you are attempting.

var data = { SubDomain: "asfsadf", ParentDomain: "asfasdf", ResellerId: "asfdsd" };

$.post('http://127.0.0.1:81/api/sites/GetDomainAvailability', data, function (results) {

    alert('Cross domain JS call achieved. Have your implementation going in here!');
}, 'json');