Basically, they created a unique 'fingerprint' of the iPhone. It was unique enough that even if you reinstalled the app, the fingerprint would still be the same. This was done, ostensibly, to prevent people from scamming them by reinstalling the app and coming over as new users? But they already have the phone number, so I don't understand the point.
In the article this is in the context of fraudsters buying used phones to fake rides in China and take advantage of incentive programs to make money. So they want to track these devices as they change hands.
Basically, they created a unique 'fingerprint' of the iPhone. It was unique enough that even if you reinstalled the app, the fingerprint would still be the same. This was done, ostensibly, to prevent people from scamming them by reinstalling the app and coming over as new users? But they already have the phone number, so I don't understand the point.