C# Web request return HTML instead JSON -

i using asihttprequest contact api. problem is returning html instead of json , have no idea why.

string url = "https://www.expert.no/tv-og-tilbehor/tv/pl-1862/"; string json = "{'siteid':2,'campaignid':0,'categoryid':1862,'startindex':0,'numbertoget':1000,'sortid':5,'isloadmore':true}";  string result = ""; using (var client = new webclient()) {     client.headers[httprequestheader.contenttype] = "application/json";     result = client.uploadstring(url, "post", json); } console.writeline(result);