If you use Apple's photo printing service you'll have to find yourself a replacement soon, as Apple is in the process of discontinuing the service. Photo Print Products was originally launched for Mac users in 2002 and first integrated into iPhoto, letting you order photo prints, albums, photo books, and calendars among other products. Later it made the move to the Photos app but was never available on the iOS mobile operating system.

It appears that not enough people were using the service. According to a message in macOS 10.13.6 Photos app final orders for Photo Print Products will have to be placed by September 30, 2018.

Luckily, Apple doesn't leave you without any printing options. The company recommends the use of third-party apps that include a Photos Projects extension. The latter is an API that was introduced with macOS High Sierra and lets photo printing services integrate their user interface into the Apple Photos app. Payment and printing are handled by the third-party provider. Currently the API is used by apps such as Mimeo Photos, Wix, GoodTimes, WhiteWall and Shutterfly.