Hey, the custom result_url(from my own S3 presigned URL) seems not working when creating animation

As my topic said, I've successfully received a 1 byte file at my S3 for each request with my custom result_url of my S3 presigned URL. however this is obviously not what I'm looking for, can you please explain why?

From what I understanding, the point of existence of result_url being a parameter is to let developers be able to save the generated live portrait to but 1 byte file is obviously incorrect to me.....