If you have a sale in that month you are liable to pay 50 rs per day (CGST 25 and SGST 25) and you have not sale invoice you can pay 20 rs (CGST 10 and SGST 25)
The Late Fees levied u/s 47 of the CGST Act 2017 is Rs. 25 per day per Act ( Rs. 25 under CGST + Rs. 25 under SGST total being Rs. 50 ) in case of a Liability Return.
In case of NIL RETURN, it is Rs. 20 per day ( Rs. 10 under CGST + Rs. 10 under SGST ).