Call POST method with RestKit v0.20

gistfile1.m

    RKLogConfigureByName("RestKit/Network", RKLogLevelTrace);
    RKLogConfigureByName("RestKit/ObjectMapping", RKLogLevelTrace);
        
    //NSString *url = @"http://0.0.0.0:5001/";
    NSString *url = @"https://asteroids-nemesis.herokuapp.com/";
        
    NSURL *baseURL = [NSURL URLWithString:url];
        
    AFHTTPClient * client = [AFHTTPClient clientWithBaseURL:baseURL];
    [client setDefaultHeader:@"Accept" value:RKMIMETypeJSON];
      
    _restKitObjectManager = [[RKObjectManager alloc] initWithHTTPClient:client];
    [_restKitObjectManager.HTTPClient setDefaultHeader:@"some-custom-header" value:@"ABC"];
    [_restKitObjectManager setRequestSerializationMIMEType:RKMIMETypeJSON];
        
    RKObjectMapping *gamerMapping = [RKObjectMapping mappingForClass:[Player class]];
    [gamerMapping addAttributeMappingsFromDictionary:@{
    @"username" : @"username",
    @"score" : @"score"
    }];
        
    RKEntityMapping *requestMapping = (RKEntityMapping*)[gamerMapping inverseMapping];
        
    RKRequestDescriptor *requestDescriptor = [RKRequestDescriptor requestDescriptorWithMapping:requestMapping objectClass:[Player class] rootKeyPath:nil];
    [_restKitObjectManager addRequestDescriptor:requestDescriptor];
    
    Player *gamer = [[Player alloc] init];
    gamer.username = username;
    gamer.score = [NSNumber numberWithLong:score];

    //Call the webservice
    [_restKitObjectManager postObject:gamer path:@"save" parameters:nil success:nil failure:nil];