When you receive an advance payment, the GST implications depend on whether it's for goods or services. For the supply of goods, GST is generally not applicable on advance payments. However, if the advance is for the supply of services, GST is applicable. In such cases, you must issue a receipt voucher and pay GST on the advance received, ensuring the calculation includes GST.
For the supply of goods, advance is not subject to GST. But if it is for supply of service, then it is subject to GST. Supplier has to issue the receipt voucher and pay GST on advance. Calculate GST taking the advance received inclusive of GST.