This is assuming you are trying to create a perfect system. The "good enough" version of this solves most Sibil Attacks[1].
If the goal of this is really as ambitious as they claim, with every single person on the planet getting UBI through it, their biometric system needs to be strict enough to not conflate two people and flexible enough to match the same iris when scanned a second time for verification. I don't believe the tech is there.