When completing an upload, the API call is done with a big timeout (21,600 seconds). It is so to handle big files.
But this is not the good way and we should do an async completion and poll for the status on a regular basis. this is not a small change but it will make big uploads more resilient and the user will not have to wait for 21,6000 second in case the server did not respond before that time.
We need to have async alls for the batch completion and the FileManager.Import calls.