A debit note may be raised for accounting purposes. However, for the purpose of GST, such a debit note will be of no relevance. Under the scheme of things, both debit note and credit note are to be issued by the supplier. Where the supplier fails to declare the details of such documents, the recipient can declare the details of the same (i.e., those issued by the supplier) and require the supplier to accept the same, in order to effect amendments in his return of outward supplies (GSTR-1). (Section 34(3) of the CGST Act, 2017).
(ICAI FAQ PUBLICATIONS 06-09-2017 TAX INVOICE, CREDIT AND DEBIT NOTES: FAQ NO. 26)