ARTG11040 - Resolution of appeal: Repayment of tax overpaid
Where the amount of tax due following resolution of the appeal is less than that originally charged, the lesser amount will be due and payable from the date of the original decision and any tax overpaid will be repaid with interest/repayment interest in line with the appropriate rules.
See CH146000+ for the guidance on repayment interest, but see CH140160 first to check which rules apply to the tax or duty you are dealing with.
It is important that repayment is made promptly to reduce the likelihood of a complaint being made.