There is a direct link to your Print products Store account in Photos in the Main Application menu:

Just to be sure - your books has at least 20 pages and no more than 100 pages? Otherwise you cannot order it.
Check also your language and region settings in the system preferences, as well as the time zone.
And try, if you can order anything at all. Try to purchase any free application from the apple STore. This will give a warning, if something is wrong with your Apple ID and the payment methid registered with the ID:
As a bow drawn at venture:
Do you have two-factor-authentification enabled? This can interfere with Photos trying to access Apple's servers.
If the two-factor-authentication is interfering it usually helps to create an app-specific password for the app you are using, in this case Photos. Then you can keep the two-step authentication active. It helped in similar cases, for example Mail, see this discussion:
Re: I am using iPhoto version 9.6 and I can no longer get an email sent with a photo attached. I get an error message saying the email did not go through because the server did not reply. I can send the photo with Mail. Help!in response to Gary Kissler
This solution is for those of you using 2-step verification for your Apple ID and are using iCloud as the mail server that you are trying to mail photos with.
I too had this issue. The problem in my case occurred because I had setup 2-step authentication for my Apple ID. If you have done this then you will get the error message "the mail server did not recognize your email/password...". To solve the problem go to:
https://appleid.apple.com
- Click "Manage Your Apple ID"
- Verify your identity with the device you selected (if this step does not show up then you have not likely set up 2-step authentication and this is not your solution)
- Click Password and Security in the left column
- Click Generate an app-specific password
- Enter iPhoto as the name of the app
- Copy the password and paste this into the password box in iPhoto where you would normally enter your apple ID (in the mail account section in iPhoto preferences).
And...voila' (I hope)