Follow this video for Setup and Use iOS 12 Siri Shortcuts on iPhone and iPad.

Compatible Models: iPhone X Plus, iPhone X, iPhone 8 (Plus), iPhone 7 (Plus), iPhone 6S (Plus), iPhone 6/6 Plus, iPhone 5S.

Or Visit this page to fix issues on Siri Shortcuts not working and activating.

https://www.howtoisolve.com/ios-12-siri-shortcuts-not-working-iphone-ipad-issues/