the software does not appear to see my face in the camera

What was you previous iOS version, that is important, because iOS 12.4 only had the following changes. Please introspect how these changes can affect what you have posted.

Phone migration

• Introduces the ability to wirelessly transfer data and migrate directly from an old iPhone to a new iPhone during setup

Apple News

• Makes downloaded issues accessible in the My Magazines section, both online and offline
• Adds all publications in Apple News+, including newspapers, to the catalog at the top of the News+ feed
• Adds the ability to clear downloaded magazine issues by selecting History > Clear > Clear All

Other improvements and fixes

• Includes a security fix for the Walkie-Talkie app on Apple Watch and re-enables Walkie-Talkie functionality

This release also includes support for HomePod in Japan and Taiwan.

Click here --> If Face ID isn't working on your iPhone or iPad Pro - Apple Support, if it still isn't working look for any spurious softwares or unauthorised apps that you may have downloaded directly from Internet

Have you had any service done to your iPhone? You will probably need to click on the Contact Support link at the top right of this page to start the service process so they can test your iPhone.