I finished a photo book in photos and would like to purchase book and I'm unable to do so HELP

Apple does no longer print books or calendars or cards since October 1, 2018.

You now have to order your books from third party services. Since your book is already ready fo r printing, save it as a PDF file and submit it to a company that can print Apple books from PDF files. See: Ordering Books and Calendars on a Mac that cannot be upgraded past El Capitan

• and this user tip: Post 9/30/2018 Printing Options for Photos - Apple Community
• And: Create and order print products in Photos with Project Extensions - Apple Support

• • Mimeo used to print for Apple and can handle PDFs created in Photos, see: https://import.mimeophotos.com
  • Also Presto Photo can print from Apple https://www.prestophoto.com
  • If you are not located in the US, there may be local printing services, which would be more economic with respect to international shipping fees and shipping time. In Germany we can use photographerbook to print existing Apple PDF files: https://www.w2p-photographerbook.de/fotobuch-aus-aperture-iphoto-fotos

See the link https://www.apple.com/macos/print-products/