An auditors' report into a pay-off of £98,000 made by Bristol City Council to its former chief executive has been described as "damning".
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.
It also found approval for the payment was not sought from the Labour-run council's human resources committee.
However, an "apparent inconsistency" between council pay policy and the terms of reference of the HR Committee meant the auditors could not "state definitively" that the council had followed the wrong process.
The Local Democracy Reporting Service (LDRS) said the auditor recommended that severance payments should not include discretionary payments.
It also advised the council should draft a policy and guidance for severance packages.
Liberal Democrat councillor Gary Hopkins described the report as "damning".
And Conservative councillor Richard Eddy said the auditors' findings "confirm that our original grave concerns about the propriety of making this huge pay-off were well-founded and completely justified".
Ms Klonowski left her £160,000-a-year post after seven months in September 2017 to look after her parents.
When the severance payment became public knowledge, opposition councillors said the sum was an "unnecessary payment" which the council could not afford or justify.
At the time, Labour mayor 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".
The council said it would be releasing its response to the auditors' findings later, and the report and the response would be considered at the next full council meeting on 19 March.