title: AFNetworking POST parameter with underscore
body: <p>This data posts perfectly fine to my web service in "Postman" but not in AFNetworking, so I know it's an issue with AFNetworking or AFNetworking's handling of NSDictionary.</p>
  
  <p>I am using the following simple code to post:</p>
  
  <pre><code>AFHTTPSessionManager *newSession = [AFHTTPSessionManager manager];
          newSession.requestSerializer = [AFJSONRequestSerializer serializer];
          newSession.responseSerializer = [AFJSONResponseSerializer serializer];
  NSDictionary *tryParameters = @{@"tripID": @"1234", @"tailNum": @"N15HEHE", @"legNum": @"1", @"file_date": @"2016"};
  [newSession POST:HTTP_POST_TRIP_DATA parameters:tryParameters progress:^(NSProgress * _Nonnull uploadProgress) {
              NSLog(@"TRY");
          } success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
  
              NSString *status = [responseObject valueForKey:@"status"];
  
              NSLog(@"RESPONSE: %@", responseObject);
  
              if ([status isEqualToString:@"success"]) {
  
                  files(YES);
              } else {
  
                  files(NO);
              }
  
          } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
              //NOT success
              files(NO);   
          }];
  </code></pre>
  
  <p>On the LAST "tryParameters" I have a key/value of "file_date" : @"2016".  That underscore seems to be the issue. If I remove the "_" (underscore) from the file_date key, everything seems to process. (Of course I get an error from my server saying that "file_date" was never given.).  But if I leave the "_" in my "file_date" key, the POST request fails and I get...</p>
  
  <pre><code>[0] (null)  @"com.alamofire.serialization.response.error.response" : (no summary)   
  [1] (null)  @"NSErrorFailingURLKey" : @"http://xxxxxxx.com/xxx/createTrip"  
  [2] (null)  @"com.alamofire.serialization.response.error.data" : (no summary)   
  [3] (null)  @"NSLocalizedDescription" : @"Request failed: unauthorized (401)"   
  </code></pre>
  
  <p>I can not figure out why the "_" is such an issue. I can read it in FROM my server in GET requests but when I try to POST, it fails.</p>