Notice the difference between what they want and what you have:
They want namespace:
http://www.idpf.org/2007/opf
but your package tag has a typo.
It defines a namespace:
http://www/idpf.org/2007/opf
So just fix the typo in your opf package tag to change:
www/idpf.org
to
www.idpf.org