Clipped from: https://taxguru.in/goods-and-service-tax/advisory-mandatory-reporting-6-digit-hsn-codes.html
Mandatory reporting of 6 digit HSN codes as per Notification No. 78/2020 – Central Tax dated 15/10/2020
As per the Notification No. 78/2020 – Central Tax dated 15th October, 2020, it is mandatory for the taxpayers to mention 6-digit HSN Codes for their outward supplies having AATO more than Rs 5 Crores.
After a few weeks of time , e-Invoice System will not accept 4-digit HSN codes. The date for blocking e-Invoice generation having HSN code as 4-digits will be intimated shortly in this portal.
So, please make necessary changes in your system to report 6-digit HSN codes to e-Invoice Portal and comply by the notification.
You may verify all your HSN codes in the ( https://einvoice1.gst.gov.in ) portal under Search–>Master–>HSN Codes and also test in the sandbox system ( https://einv-apisandbox.nic.in ).
In case the 6 digit HSN code is not available, you may raise a ticket at Helpdesk so that it can be included in the system.