A pay-off of almost £100,000 made by Bristol City Council to its former chief executive was not a contractual obligation, according to auditors.
Bristol Mayor Marvin Rees insisted Anna Klonowski was entitled to the cash when she left in September 2017.
But the council's auditors said it was "inappropriate" for the authority to say the payment was contractual.
Deputy Mayor Craig Cheney says the payment was made in line with the legal advice at the time.
The BBC originally understood Ms Klonowski received £70,000, but the official audit shows the exact figure is £98,000.
She left her £160,000-a-year post after seven months in September 2017 to look after her parents.
When the payment became public knowledge, opposition councillors said the sum was an "unnecessary payment" which the council could not afford or justify.
At the time, Mr Rees, said her contract was agreed and "all processes were open and transparent".
He also denied she was paid any additional sum, but instead "left the council on the terms of the contract agreed by the HR committee".