Error: "Guided Access app unavailable. Please contact your administrator"

When a single app mode configuration is applied to a device and the specified app is not already installed, the device will display the following message:

Guided Access app unavailable. Please contact your administrator

The device will remain non-functional until single app lock is disabled on the device. iOS does not currently allow apps to be installed or updated while single app lock is enabled, so the single app mode configuration must be disabled before installing the necessary app.