AFNetworking POST METHOD cannot pass parameter

Sorry, I am new to AFNetworking. I was working on a project to add some post parameters to a server. Here is my code:

NSString *server_url=[NSString stringWithFormat:@"%@/AccessPoint_NewPlayerRegistration.php",server];

AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
manager.responseSerializer = [AFHTTPResponseSerializer serializer];

AFHTTPRequestOperation *operation =
[manager

 POST: server_url
 parameters: @{@"captcha":captchaTextField.text,
               @"player_name":nameTextField.text,
               @"player_time_now":[NSNumber numberWithInt:[[NSDate date] timeIntervalSince1970]]
               }

 success:^(AFHTTPRequestOperation *operation, id JSON){

     NSString *text = [[NSString alloc] initWithData:JSON encoding:NSUTF8StringEncoding];
     NSLog(@"%@",text);


 }

 failure:^(AFHTTPRequestOperation *operation, NSError *error){
     NSLog(@"%@",error);
 }
 ];

[operation start];

The operation was successful but the server send back an error message which shows there are no parameters in the request. My parameters cannot send to server through post method.

I have been working on this problem for days:( Thanks in advance for the help.