iOS AFN向接口端传递JSON数据

NSDictionary *body = @{@"snippet": @{@"topLevelComment":@{@"snippet":@{@"textOriginal":self.commentToPost.text}},@"videoId":self.videoIdPostingOn}};
NSError *error;
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:body options:0 error:&error];
NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];

AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];

NSMutableURLRequest *req = [[AFJSONRequestSerializer serializer] requestWithMethod:@"POST" URLString:[NSString stringWithFormat:@"https://www.googleapis.com/youtube/v3/commentThreads?part=snippet&access_token=%@",[[LoginSingleton sharedInstance] getaccesstoken]] parameters:nil error:nil];

req.timeoutInterval= [[[NSUserDefaults standardUserDefaults] valueForKey:@"timeoutInterval"] longValue];
[req setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
[req setValue:@"application/json" forHTTPHeaderField:@"Accept"];
[req setHTTPBody:[jsonString dataUsingEncoding:NSUTF8StringEncoding]];


[[manager dataTaskWithRequest:req completionHandler:^(NSURLResponse * _Nonnull response, id  _Nullable responseObject, NSError * _Nullable error) {

    if (!error) {
        NSLog(@"Reply JSON: %@", responseObject);

        if ([responseObject isKindOfClass:[NSDictionary class]]) {
              //blah blah
        }
    } else {
        NSLog(@"Error: %@, %@, %@", error, response, responseObject);
    }
}] resume];