GST is payable on advances received from customers, what is provision for GST where part payment (5% or 10%) is payable after three / six months of receipt & acceptance of goods and balance 10% or 20% payment after successful installation & commissioning or performance of equipment.
GST for differed (after commissioning & acceptance etc) payment.
GST applies on receipt of advances and on invoicing for deferred payments; suppliers must issue a receipt voucher when advance is received and a tax invoice according to statutory timing rules, while recognizing that continuous supply timing provisions may not govern discrete goods contracts with milestone payments, and that enabling notifications prescribing invoice timing were not yet issued. (AI Summary)
TaxTMI 
