legal ground
Article 51 of the Law on the Administration of Tax Collection
Upon discovery, the tax authorities shall immediately refund the tax overpaid by taxpayers; If a taxpayer finds out within three years from the date of final settlement of the tax, he may request the tax authorities to refund the overpaid tax and add interest on the bank deposits during the same period, and the tax authorities shall immediately refund it after timely verification; If it involves withdrawing the treasury, it shall be returned in accordance with the provisions of laws and administrative regulations on treasury management.