100% Discount on Invoice

Yes. If you do not charge the GST on sale then you will have to reverse the GST which was used while purchase of the goods. 

hope you got the point ..its better to have deposit gst with giving 100% discount than reverse the input tax

hope you got the point ..its better to have deposit gst with giving 100% discount than reverse the input tax

But, where it has been written in GST Act or Rule  when you do not charge gst then you should reverse ITC.

I supied a water purification plant to my customer. It was invoiced and was included in GSTR1 for that month. However , while commissioning the plant, it was found that 50 litres more of ion exchange resin must be added again to get the desired result. I cannot invoice this to the recipient as it is my scope to get the result, for the quoted price.and material supplied. How I can handle this supply. Should I pay GST against this 

rather than giving it free and creating ambiguity, why not sell the product/ service for a promotional offer of Rs. 1 and then pay the GST on it also.