Article R2192-34 of the French Public procurement code
In the event of disagreement over the amount of an advance payment or the balance, payment is made within the time limits set out in articles R. 2192-10 and R. 2192-11 on the provisional basis of the sums accepted by the contracting authority. When the sums thus paid are less than those finally due to the creditor, the latter is entitled to interest on arrears calculated on the difference.