Generally speaking, 0 for the readyState of the XMLHttpRequest means that the request is still not initialized. Prior to triggering the upload event, the XHR is created and if the upload is not prevented, open method is invoked and the readystatechange should be fired.
So, I would need more details on the matter - configuration of the upload or a sample project illustrating the issue - in order to diagnose the cause of the issue. The only reason that I could come up is if the upload gets prevented somewhere in your project logic, and thus, leading to not loading the xhr.
The example from this thread could be observed and run in our documentation:
I am looking forward to your reply.
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