25 April 2019
You can issue till 20th October of the following FY or date of filing Annual return , whichever is earlier
Supplier who is issuing credit note/Debit Note will declare the details of credit note/Debit Note issued under GSTR-1 of that month or later but not later than September following the end of the financial year in which such supply was made, or the date of furnishing of the relevant annual return, whichever is earlier.