Registration is mandatory if the turnover is >₹20 lacs (except special category states). Voluntary registration can be applied for even without crossing the turnover limit.
GST REGISTRATION IS OPTIONAL BUT NOT COMPULSORY. LETS TAKE AN EXAMPLE A PERSON ENGAGED IN BUSINESS AND TURNOVER OF ONLY 50000 DURING A FINANCIAL YEAR IS NOT REQUIRED TO REGISTER UNDER THE GST ACT.