Vendor ID Error
I am trying to publish abook through Ibook author and I keep getting "Missing Required file: Vendor Identifier". I have gone back to the first page on ITunes Producer where you insert the ISBN number which I have inserted but the Vendor ID field remain greyed out and I cannot insert anything. How do I get around this? Do I have to insert the ISBN number in the actual book? If so can anybody tell me how to do this in IBooks Author as I cannot find out how to do it anywhere.
Thanks
Soparch
iBook