Harmonised System of Nomenclature (HSN) code is used for the classification of goods. A 4-digit code is to be used in the invoices by the Taxpayers with a turnover upto Rs. 5 crores. While the taxpayers whose turnover is more than Rs. 5 crores are to use 6-digit code. This requirement has been made mandatory w.e.f 1st April, 2021.