But the former departmental secretary told a royal commission hearing into the scheme she was not pressured by coalition ministers at the time to do so.
Kathryn Campbell was secretary of the human services department when robodebt was proposed and later the social services department while it was operating.
The robodebt scheme ran from 2015 to 2019 and introduced debts calculated by income averaging using tax office data.
Ms Campbell was questioned on Tuesday about why a ministerial brief in 2015 said there was no change to the way income was assessed or how overpayments were calculated, even though there had been.
Asked if the reason she did not notice the change was because she did not pay close attention to the document, Ms Campbell said she "could not recall".
She agreed it was a significant oversight.
"As the secretary, I was responsible for what happened within the department (and) I did not notice the change in the drafting," she said.
"Was there pressure placed on me ... to say that no legislation (change) was required? No."
Assisting counsel Justin Greggery proposed the department had changed the language in the brief so it could avoid having to change legislation required to implement the measure, which would have been difficult to pass through parliament.
Ms Campbell rejected this suggestion.
"I have never been in a department that has sought to mislead the government, nor have I ever been involved in an operation that seeks to mislead the government," she said.
The commission is examining how the scheme was allowed to continue, given significant concerns about its legality raised by early 2017.
Ms Campbell told the commission she did not consider the fairness of income averaging because her focus was on ensuring customers had an opportunity to engage with the system.
Asked if she considered the possibility the debt recipients did not engage with the department, Ms Campbell said she didn't until January 2017, two years after the program started.
She said debt letters were put on hold between January and August 2017 to allow the department to change the system and make it more "user friendly".
"I thought fairness had been achieved, procedural fairness, by ensuring the recipient had received the correspondence," she said.
Commissioner Catherine Holmes asked if Ms Campbell considered whether the proposal was "intrinsically unfair", regardless of whether legislation had passed to allow it to happen.
"At that time I thought it was legal. I now know it not to be the case," Ms Campbell replied.
Last week the commission heard from Ms Campbell's replacement as human services secretary, Renee Leon, who said her predecessor "took credit" for the robodebt scheme.
"I understood it to have been something that she thought of," Professor Leon said.
"She had recommended to me that I should look further in the compliance area because that's where there was money to be found ... she had had great success in doing that by coming up with the Online Compliance Interventions."
