Please set the invoice view to Indian GST in system settings.
Indian GST is being calculated as following:
Purchases: Set the business state in system setting to check if the IGST or CGST & SGST as if the business state is different than the supplier state (full tax) IGST will be applied and if the states are same it will be (1/2 tax) CGST & (1/2 tax) SGST.
Sales: System will check the biller state and customer state to calculate the GST. If they are from same state it will be (1/2 tax) CGST & (1/2 tax) otherwise (full tax) IGST.