Turnover below 1.5

From 1.4.2021, it is compulsory to mention HSN/SAC code on invoices issued to B2B customer for entity's with turnover up to Rs.5 crores. Non-furnishing HSN in GSTR-1 might attract a general penalty of maximum Rs.25,000 each for CGST and SGST-Section 125

Yes, penalty can be levied by the department but the chances are less I think. Just ensure to include HSN code from now onwards.

At present no penalty is being charged but ensure compliance from next return.