How to pass variable from flutter to native objective c

I have found plenty of information on passing data from flutter to android using method channel but none for objective c. I understand calling functions, but not passing data. Below is an example of what I have.

  Future<void> _uploadImage(String filePath) async {
    try {
      await platform.invokeMethod('uploadImage', {"filePath": filePath});
    } on PlatformException catch (e) {
      print("Failed to get token: '${e.message}'.");
    }
  }

else if([@"uploadImage" isEqualToString:call.method]){
      DBUserClient *client = [DBClientsManager authorizedClient];
      NSString *filePath = call.arguments(@"filePath");
      NSLog(filePath, result);
      NSData *fileData = [filePath dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:NO];

    [[[client.filesRoutes uploadData:filePath inputData:fileData]
      setResponseBlock:^(DBFILESFileMetadata *result, DBFILESUploadError *routeError, DBRequestError *networkError) {
          if (result)
          {
              NSLog(@"%@\n", result);
          } else
          {
              NSLog(@"%@\n%@\n", routeError, networkError);
          }
      }] setProgressBlock:^(int64_t bytesUploaded, int64_t totalBytesUploaded, int64_t totalBytesExpectedToUploaded) {
          NSLog(@"\n%lld\n%lld\n%lld\n", bytesUploaded, totalBytesUploaded, totalBytesExpectedToUploaded);
      }];
    }

    else{
      result(FlutterMethodNotImplemented);
    }
}];
  return [super application:application didFinishLaunchingWithOptions:launchOptions];
}

To clarify, the bottom set of code written in objective-c is definitely not correct, but I've been trying to piece it out. I have the images path and I am trying to upload it to Dropbox. Main issue is that the filePath is not reaching the method channel. NSString *filePath = call.arguments(@"filePath") isn't an actual function call.