Debit notes in GSTR1

In Form GSTR-3B, value of taxable supplies = value of invoices + value of debit notes – value of credit notes + value of advances received for which invoices have not been issued in the same month – value of advances adjusted against invoices.

So, output tax will be after reduction of credit note issued by the supplier.

In GSTR-1, if you don’t fill the credit/debit note details issued by you, then the output tax liability will be shown as inflated and won’t match with the liability declared in GSTR-3B.