Json iOS AF2.0 umlaut错误

我正在使用AFNetworking 2.0将数据发送到我的API json。除了用像äüö这样的德语字母发送数据外，一切正常

有人知道问题出在哪里吗？。问题不在于API，因为我是在Android上做的，而且很有效

这是我的密码：

  - (void)createItem:(MyItem*)newItem image:(UIImage*)image complete:(void (^)(NSInteger responsecode, NSString *hash, NSDictionary *reason))completeBlock {

    NSData *imageData = [NSData new];
    if(image != nil) {
        imageData = UIImageJPEGRepresentation(image, 0.5);
    }

    NSMutableDictionary *parameters = [[NSMutableDictionary alloc]initWithCapacity:2];
    [parameters newItem.address forKey:@"address"];
    [parameters newItem.email forKey:@"email"];

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

    AFHTTPRequestOperation *op = [manager POST:postUrl parameters:parameters constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
        [formData appendPartWithFileData:imageData name:@"photo" fileName:@"photo.jpg" mimeType:@"image/jpeg"];

    } success:^(AFHTTPRequestOperation *operation, id responseObject) {
        NSString *hash = operation.responseString;
        completeBlock([operation.response statusCode], hash, nil);

    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        completeBlock([operation.response statusCode], nil, nil);
    }];
    [op start];

}