HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://api.roblox.com/signup/v1");

        request.KeepAlive = true;
        request.Accept = "application/json, text/plain, */*";
        request.Headers.Add("Origin", @"https://www.roblox.com");
        request.UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.99 Safari/537.36";
        request.ContentType = "application/x-www-form-urlencoded";
        request.Referer = "https://www.roblox.com/account/signupredir";
        request.Headers.Set(HttpRequestHeader.AcceptEncoding, "gzip, deflate, br");
        request.Headers.Set(HttpRequestHeader.AcceptLanguage, "en-US,en;q=0.8");
        request.Headers.Set(HttpRequestHeader.Cookie, @"RBXSource=rbx_acquisition_time=11/20/2016 4:16:17 PM&rbx_acquisition_referrer=&rbx_medium=Direct&rbx_source=&rbx_campaign=&rbx_adgroup=&rbx_keyword=&rbx_matchtype=&rbx_send_info=1; RBXViralAcquisition=time=11/20/2016 4:16:17 PM&referrer=&originatingsite=; GuestData=UserID=-786589586; RBXMarketing=FirstHomePageVisit=1; _ga=GA1.2.1124241181.1479680169; __gads=ID=2f32111c4a67df96:T=1479932982:S=ALNI_MYQrw_wu6veOAM4iM4ic50xkPn2JA; RBXEventTrackerV2=CreateDate=11/24/2016 8:10:20 PM&rbxid=184130891&browserid=5729346186; rbx-ip=; RBXImageCache=timg=30336534386264332D616236352D343162662D383061312D3763656637363738396534642535302E3133362E3138312E3231362531312F32312F323031362031313A33343A303320504DE75B95121DA744C64A041A6EAC747C4F1DD27F41; __utmt_b=1; __utma=200924205.1124241181.1479680169.1480038327.1480042238.14; __utmb=200924205.26.10.1480042238; __utmc=200924205; __utmz=200924205.1480022244.12.3.utmcsr=web.roblox.com|utmccn=(referral)|utmcmd=referral|utmcct=/catalog/");

        request.Method = "POST";
        request.ServicePoint.Expect100Continue = false;

        string body = @"isEligibleForHideAdsAbTest=False&username=f3400324f2&password=PASSWORD&birthday=18+Sep+1998&gender=2&context=RollerCoasterSignupForm";
        byte[] postBytes = System.Text.Encoding.UTF8.GetBytes(body);
        request.ContentLength = postBytes.Length;
        Stream stream = request.GetRequestStream();
        stream.Write(postBytes, 0, postBytes.Length);
        stream.Close();

        response = (HttpWebResponse)request.GetResponse();