Former prime minister Scott Morrison will appear at a royal commission into the failed robodebt scheme on Wednesday.
The commission is attempting to establish why the changes to welfare debt protocol were adopted, despite concerns over their legality.
Mr Morrison was involved with implementing the scheme in 2015, when he was social services minister.
Records show Mr Morrison signed a department document that included the concerns, which were absent when the policy was later presented to cabinet for consideration.
Between 2015 and 2020 the scheme wrongly recovered more than $750 million from 381,000 people, with several victims taking their lives while being pursued for the false debts.
Former foreign minister Marise Payne appeared as a witness before the commission on Tuesday.
Senator Payne was human services minister at the time the program was formulated and oversaw the creation of department briefings for Mr Morrison, who was her senior minister.
She said she had no knowledge of why the legal issues flagged in earlier briefings were omitted from the final policy proposal.
"How did the identification of the problem ... drop off the radar by the time it seems (cabinet) considered the proposal?" senior counsel assisting Justin Greggery KC asked Senator Payne.
"I don't know the answer to that question and I say that in all transparency," she said.
"There is an expectation, however, that when agencies advise you, on the face of a brief, that they are working together to address these issues."
When asked who held responsibility for advancing the concerns, Senator Payne said ministers were always "ultimately responsible" but must receive advice from their departments.
© AAP 2022