I have ordered several copies of my book, but I don't see an approval button at the bottom of the Distribution Serviceroof Copy page.
Look at the top of the Page for Revise/Approve.
Approve is only there if you have selected the General option and your book is one of the options that can have a free ISBN and Distribution.
It's also possible that your Project is still in Draft. If so then complete the Draft version.
Myself and my friend combined know everything there is to know, but he's not here.