I thought that was weird (I mean no other cloud provider asked for it but okay). I uploaded anyway because I thought it’s in EU so they at least have better privacy laws so they may end up deleting it later from their systems but I immediately got rejected. Not sure why no reason specified. So now they have my passport copy page without me having an account.
Oh well, seems like either they have an overly aggressive spam filter that gets false positives or they don’t really like accepting signups from Asia