Laravel - Pass uploaded filename to new function - php

Question

I'm using Laravel 5.3 and need to upload an xml file and then submit the contents to an api. The client wants it as 2 buttons/user functions where the user should first upload the file and then with a second click submit the contents.
The uploading is working fine and the xml reading and submitting to api is also working properly. I just can't get my upload controller to pass the filename over to the submitting controller. There is no need to store the filename for future use and the processes will follow each other - ie user will upload one file and submit, then upload next file and submit.
Any help would be highly appreciated
upload function:
public function handleUpload(Request $request)
{
$file = $request->file('file');
$allowedFileTypes = config('app.allowedFileTypes');
$rules = [
'file' => 'required|mimes:'.$allowedFileTypes
];
$this->validate($request, $rules);
$fileName = $file->getClientOriginalName();
$destinationPath = config('app.fileDestinationPath').'/'.$fileName;
$uploaded = Storage::put($destinationPath, file_get_contents($file->getRealPath()));
if($uploaded) {
$file_Name = ($_FILES['file']['name']);
}
return redirect()->to('/upload');
}
submit function:
public function vendorInvoice()
{
$fileName = $file_Name;
$destinationPath = storage_path('app/uploads/');
$xml = file_get_contents($destinationPath.$fileName);
$uri = "some uri";
try {
$client = new Client();
$request = new Request('POST', $uri, [
'Authorization' => '$username',
'ContractID' => '$id',
'content-type' => 'application/xml'
],
$xml);
$response = $client->send($request);
}
catch (RequestException $re) {
//Exception Handling
echo $re;
}
}