I was trying just the normal way without the upload document procedure.

I just got off the phone with an agent, he actually made me press "Submit" 3 times with an empty form, and on the 3rd time I get a new dialog asking me to submit my documents. I uploaded a picture of my boarding pass and my email ticket confirmation and submitted successfully. Neat trick that will hopefully be useful to others.

Just waiting for it to be processed, the form says it can take up to 3 week longer than a normal submission.