Whether GST on Discount?

What about GST charged in the invoice?

Hence their will be no effect on goods and purchase value will be 100 only as per inventory base and the 2 rs discount would be treated as indirect income. No effect on purchase rate.

Gst can be reduced only if
1 Discount was incorporated in invoice, or
2 At time of supply there was agreement for such discount (i.e To be provided at some later stage on occurrence of event or fulfilment of conditions)
Since by your stated facts it doesn't fall in either of points therefore gst cannot be reduced
only option is credit note