idHTTP.Post

procedure TForm4.Button2Click(Sender: TObject);
var
 sResponse: string;
 EnvStr : TStringStream;
begin
 EnvStr := TStringStream.Create(Memo.Text, TEncoding.UTF8);
 try
  idHTTP.Request.ContentType := 'application/json';
  try
   sResponse := idHTTP.Post(EditURL.Text, EnvStr);
  except
    on E: Exception do
      ShowMessage('Error on request: '#13#10 + e.Message);
  end;
finally
  EnvStr.Free;
  MemoRet.Text := sResponse;
end;