can you be a little more specific as to what you mean by you cannot write files?
iOS sandboxes third party apps so you can only access pictures and videos stored in the iOS native camera roll (native photos app)
From the media drive main screen select videos or photos. Then at the bottom of the page you will see and option to view from the drive or the iOS device. Select the iOS device then you will see the pictures or videos stored in the camera roll of the iOS device. select the items you want to transfer and then select the share button at the bottom and choose save to media drive. All files will be saved in to the media drive upload folder.
