HELLO....
IF YOU HAVE TO FILE NIL GST RETURNS LATE FEES WILL BE AUTOMATICALLY CALCULATED BY SYSTEM. YOU HAVE TO SPEND MINIMUM 10000 PER RETURN. IF LUCKY AMNESTY SCHEME MAY APPLY. BUT YOU WILL GET TO KNOW EXACT AMOUNT OF LATE FEE PER MONTH PER RETURN WHILE FILING ONLY.
FIRST CHCEK REGISTRATION STATUS OF YOUR CLIENT.
IF ACTIVE YOU CAN FILE RETURNS AND LATE FEES WILL BE CALCULATED BY GSTIN ITSELF.
IF GSTIN HAS BEEN CANCELLED ON RETROSPECTIVE I.E., FROM DATE OF LAST FILING MONTH THEN YOU CANNOT FILE RETURNS.
BEST POSSIBLE SOLUTION HERE IS ASK YOUR CLIENT TO TAKE NEW GST REGISTRATION WITH PAN DETAILS OF RELATED PERSONS WITH NEW PRINCIPAL PLACE OF BUSINESS.