尝试一下：

NSData *jsonData = [NSJSONSerialization dataWithJSONObject:parameters options:0 error:nil];
NSString *parametersString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];

[manager GET:kURLChangeSetting
  parameters:@{@"setting" : parametersString}
     success:^(AFHTTPRequestOperation *operation, id responseObject) {
         // code
     } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
         /// code
     }];