asp.net - Sending Push Notification to multiple android devices using asp .net -

i'm trying send push notifications multiple android devices.

for 1 device working, when tried add multiple device registrationids not; gcm returns error=invalidregistration

var message = tmessage.text; //message text box                var title = ttitle.text;             string stringregids = null;             list<string> regids = new list<string>();             regids.add(redidemulnew);             regids.add(regidmobilenew);              stringregids = string.join("\",\"", regids);                 webrequest trequest;              trequest = webrequest.create("https://android.googleapis.com/gcm/send");              trequest.method = "post";              trequest.contenttype = " application/x-www-form-urlencoded;charset=utf-8";              trequest.headers.add(string.format("authorization: key={0}", applicationid));              trequest.headers.add(string.format("sender: id={0}", sender_id));             string postdata =              "collapse_key=score_update&time_to_live=108&delay_while_idle=1&data.message="               + message + "&data.title=" + title + "&registration_id=" +                  stringregids + "";               byte[] bytearray = encoding.utf8.getbytes(postdata);              trequest.contentlength = bytearray.length;              stream datastream = trequest.getrequeststream();              datastream.write(bytearray, 0, bytearray.length);              datastream.close();              webresponse tresponse = trequest.getresponse();              datastream = tresponse.getresponsestream();              streamreader treader = new streamreader(datastream);              string sresponsefromserver = treader.readtoend();   //get response gcm server.              lbresponse.text = sresponsefromserver;      //assigning gcm response label text               treader.close();              datastream.close();             tresponse.close(); 

i suspect below code has issue:

string stringregids = null; list<string> regids = new list<string>(); regids.add(redidemulnew); regids.add(regidmobilenew); stringregids = string.join("\",\"", regids);  

both device registration ids valid, have checked push notifications individually.

thanks

after searching long time found "multicast messages (sending more 1 registration ids) allowed using http json format only"

here reference https://developers.google.com/cloud-messaging/server-ref#table1

and example http://labs.distriqt.com/post/1223

string postdata = "{ \"registration_ids\": [ \"" + stringregids + "\" ], " + "\"data\": {\"title\":\"" + title + "\", " + "\"message\": \"" + message + "\"}}";