Device Identifier
The Device Identifier is a 32 character alpha-numeric string randomly assigned at the time that the app is first launched. It is unique to each app on each device.
In NIH Toolbox V3, tap "Help & Support" at the bottom corner of the screen, then scroll to the bottom. The Device Identifier is under the "Diagnostic Information" section.
In NIH Toolbox V2, go to "Help & Support" page by tapping on the "?" on the lower right corner of the app. The Device Identifier is under the "Diagnostic Information" section.