How to send a push notification to APNS via TIdHttp indy component?

Question

I have been using Indy's TIdTCPClient component successfully for quite a while now to send push notifications to my mobile app users. Lately, due to new push notification requirements of Apple, this feature has stopped being functional for iOS users.

For the past three days, I've been trying to reconstruct this function by using the TIdHTTP component instead, following the new HTTP/2 format advised by Apple to send push notifications. Unfortunately, I've yet to come up with something operational.

Here's my failing code:

procedure TForm5.BtnPushClick(Sender: TObject);
var
  vHTTP: TIdHTTP;
  SslIOHandlerHTTP : TIdSSLIOHandlerSocketOpenSSL;
  RequestBody: TStream;
  ResponseBody, vCertFileName: string;  
  vJsonToSend : TStringStream;
begin
  try
    vCertFileName     := 'apns-dist.pem';
    vIdHTTP := TIdHTTP.Create(nil);
    SslIOHandlerHTTP := TIdSSLIOHandlerSocketOpenSSL.Create(vHTTP);
    SslIOHandlerHTTP.OnVerifyPeer  := SslIOHandlerHTTP1VerifyPeer;
    SslIOHandlerHTTP.OnGetPassword := SslIOHandlerHTTP1GetPassword;
    SslIOHandlerHTTP.SSLOptions.CertFile    := vCertFileName;
    SslIOHandlerHTTP.SSLOptions.KeyFile     := vCertFileName;
    SslIOHandlerHTTP.SSLOptions.Method      := sslvTLSv1_2;
    SslIOHandlerHTTP.SSLOptions.Mode        := sslmBoth;
    SslIOHandlerHTTP.SSLOptions.SSLVersions := [sslvTLSv1_2];
    SslIOHandlerHTTP.SSLOptions.VerifyMode := [sslvrfPeer];
    SslIOHandlerHTTP.SSLOptions.VerifyDepth := 2;
    //--
    vHTTP.Request.CustomHeaders.AddValue(':method', 'POST');
    vHTTP.Request.CustomHeaders.AddValue(':scheme', 'https');
    vHTTP.Request.CustomHeaders.AddValue(':path', '/3/device/111890052839d3ed4f596c94712329e20812464afe30ebd28487c4e65986c6f0');
    vHTTP.Request.CustomHeaders.AddValue('host', 'api.push.apple.com');
    vHTTP.Request.CustomHeaders.AddValue('apns-id', 'eabeae54-14a8-11e5-b60b-1697f925ec7b');
    vHTTP.Request.CustomHeaders.AddValue('apns-push-type', 'alert');
    vHTTP.Request.CustomHeaders.AddValue('apns-expiration', '0');
    vHTTP.Request.CustomHeaders.AddValue('apns-priority', '10');
    vHTTP.Request.CustomHeaders.AddValue('apns-topic', 'com.TS.JACK');
    //--
    vHTTP.IOHandler           := SslIOHandlerHTTP;
    vHTTP.Request.Accept      := 'application/json';
    vHTTP.Request.ContentType := 'application/json';
    vHTTP.HTTPOptions         := [hoForceEncodeParams];
    vHTTP.ProtocolVersion     := pv1_1;
    SslIOHandlerHTTP.PassThrough := true;

    vJsonToSend := TStringStream.Create('{ "aps" : { "alert" : "Hello" } }', TEncoding.UTF8);
    ResponseBody := vHTTP.Post('https://api.push.apple.com', vJsonToSend);
  except
    on E: Exception do
    begin
      Memo1.Lines.Add(IntToStr(vHTTP.ResponseCode)+':' + E.Message);
    end;
  end;