A "normal" iTunes Store Apple ID/Account does NOT allow you to upload to the store.
iTunes Producer looks for you registered book sellers ID
Have you actually opened a book sellers account with Apple?
Have you opened an iTunes Connect Account?
If the answers are no... https://itunesconnect.apple.com/WebObjects/iTunesConnect.woa/wa/bookSignup
Open the link and click on Get Started > select the free or paid book account and proceed through the sign up process.
Its advisable to use a different username/PW and email for a book sellers account and if you intend to have free and paid books, you will need separate accounts?IDs
You will be asked for your website URL ( address) if you dont have a website... Facebook is a ready answer. Apple sees this as a "Support" contact path.
If you want to sell books, you will also need an EIN number from the US tax
If you have done all this and still have problems, you first need to check and confirm all your details are correct.