credit note

You are not required to issue debit note. Credit note issued by your supplier is sufficient. Your supplier will show the credit note details in his GSTR-1.

if credit note and invoice is in same month - Show net input tax credit (Input tax credit as per nvoice - Input tax credit as per credit note)

if the credit note is issued in subsequent month - Then you need to reduce your eligible input tax credit to the extent of GST mentioned in credit note.

Debit note issued by customer does not have validity under GST. Supplier shall issue debit note or credit note under GST Law, to reduce or increase his output tax liability. Based on which the customer can reduce or increase his input tax credit.