Q: Unable to purchase photo book

  Now when I go to 'buy' it says I am not connected to the internet.

What is the exact error message?

is the PDF preview of your book correct?  Sometimes you get "Try again later" error messages, if your book contains items that cannot be processed, like missing or corrupted photos.

To make a PDF preview see:   Preview a print project in Photos, iPhoto, or Aperture to avoid issues - Apple Support

If the preview is fine, but you are still getting error messages, check, if you have a firewall enabled, or an antivirus filter issues active, that could intercept the connection to the Mac Print Products Store.