A Tory council briefly lost £9.1 million when a staff-member "mis-typed" its bank account details.
The millions were clawed back- but Hertfordshire County Council lost £300 in interest after the funds temporarily vanished.
The money was due to be transferred back into a council account on August 7, before short-term investment into a market fund, according to the local authority's audit.
However, a staffer typed in two wrong digits as they were transcribing the council's bank account details and the error was missed.
Instead of the money being transferred, it was instead returned to the council account it had sent from two days later - and two days after the payment was due.
According to the council's own report, no one appeared to notice when £9.1m hadn't arrived in the bank account it was destined for on the day it went missing.
The details of the treasury control failure were contained in a report put before the council's audit committee's Friday meeting.
"Because invalid bank account details were used, the £9.1m was returned to the issuer," the report said. "The County Council received the misdirected funds on 9th August 2019.
"The financial impact was a loss of interest of approximately £300. No additional overdraft fees were incurred, and there were no other breaches of TM (treasury management) strategy as a result of the error."
The failures were identified as the "incorrect account number" being entering, and no-one noticing when the funds didn't arrive on the day they were due.
The account number used on the request was mis-typed, the report said.
The instructions were presented for signing on the basis a second staffer had checked them for accuracy - but that either didn't take place or the error was not picked up, the report continued.
The council's treasury contacted the bank to trace the funds, and correct payment instructions were reissued.
Payment procedures had been overhauled since the incident "due to the serious nature" of the error, the report continued.
A draft report on the review's findings said there are effective controls were now in place, and added some recommendations to make changes by March to prevent the mistake being repeated.
According to the Local Democracy Reporting Service, the committee's chair, Cllr Frances Button, a Conservative, said while the error was "regrettable", and 100 per cent performance was expected, the error was one out of many thousands of smooth payments.
She added that she was proud of the council's finance officers for picking up the error and fixing it immediately, and praised their work enhancing finance controls in the aftermath, reports the Welwyn Hatfield Times .
The Mirror recently reported on the case of a man who lost £193,000 when he got his bank account wrong as he was arranging his inheritance after his father died.
The error highlighted how account number errors can go terribly wrong, after the customer who received his money refused to return it and the bank told Cambridge man Peter Teich, 74, it couldn't force the man to give the cash back.
Mr Teich was forced to pursue the customer through the courts after Barclays said it could not compel the man to return his inheritance.
The bank eventually agreed to cover the disabled pensioner's £46,000 in legal costs and gave him £750 in compensation after he had to go through a costly court battle.
