A council criticised for underpaying a couple who cared for their grandchild has been told to change its policy after a failed court challenge.
The pair complained because the allowance they received from Rochdale Council did not increase in line with fostering rates.
A watchdog ruled they were entitled to an extra £13 a week but the council took the case to the High Court.
The council said it was "very sorry" and would correct any payment errors.
The BBC has asked Rochdale Council how much the legal action has cost.
The case involved grandparents from Rochdale who were granted a Special Guardianship Order in 2011 over their grandchild.
Under the order, the courts appoint someone, often extended family members, to be a child's special guardian who will then become responsible for all day to day decisions about the child.
The couple complained to the Local Government and Social Care Ombudsman because their allowance did not increase in line with fostering allowance rates nor were they given the age band increase for the child as agreed.
As a result, they continued to receive the Level 1 fostering allowance of £119.18 a week instead of the enhanced rate £132 a week.
'Put right errors'
The ombudsman found the council's allowance policy, which had not been agreed by any formal committee, was not in line with statutory guidance, case law, or its own internal legal advice.
Its report asked the council to calculate and make backdated payments going back to November 2013.
It also recommended the council reconsiders its policy and and compensates all other special guardians affected by the error.
Speaking after the High Court ruling, ombudsman Michael King said it had offered guidance to councils in 2013 and 2018 after finding a number of families had not been treated fairly.
"Special guardianship orders offer invaluable stability to children who, for whatever reason, cannot live with their birth parents.
"We sincerely hope [Rochdale Council] will now honourably accept our recommendations to correct the error and protect other families in the future."
The council said it was "very sorry for this payment error and the inconvenience caused" and was ordered to pay almost £2,500 in court costs.
Director of Children's Services, Gail Hopper, said it would consult a new policy and "put right any errors... by making appropriate compensatory payments".