To clarify the Robodebt was to recover instances of un-reported and under-reported earnings. The debts are real, but the way they imposed those debts were not well handled.

Usually, there's an income check. People are asked to call in and supply payslips for a period, and then those amounts are applied to the correct entitlement period according to the periods they're within. Working credits or student credits that normally offset these are applied accordingly as well.

What happened, instead, was the earnings were apportioned equally over a period of time. This didn't take into account periods of earning below the threshold, or correctly balancing credits, which lead to people getting a lot of small debts in entitlement periods instead of debts correctly apportioned.

So in their bold actions to retrieve the debts, they overstepped and caused so many issues that they had to respond to a class action lawsuit by dropping the debts completely, losing tens of millions in revenue from legitimate fraud and under-reporting.