I issued a GST invoice with a wrong amount. Should I cancel it or issue a credit note?

It depends on whether the invoice has already been reported.

• Not yet filed in GSTR-1: you can correct or cancel it in your records and report the right invoice in that return.
• Already reported, and the error is only in how it was recorded (for example a typing mistake in the value), with the actual transaction unchanged: correct it through the amendment table of a later GSTR-1.
• Already reported, and the taxable value or tax actually needs to go down: issue a credit note under Section 34 of the CGST Act and report it in GSTR-1. If the amount needs to go up, issue a debit note.

For an e-invoice, the IRN can be cancelled on the portal only within 24 hours of generation. After that, a credit note is the route. Credit notes and amendments must be made by 30 November following the end of the financial year or the date of filing the annual return, whichever is earlier. Please confirm the right route for your case with your CA.