Yes, it is possible to cancel already generated Invoice Registration Number (IRN). It is important to note that, IRN cancellation is allowed only within 24 hours of its generation.
After 24 hours from the invoice generation, the IRN cannot be cancelled and in this case the supplier has to issue either a Debit or Credit note or amend the GSTR-1 Form.
IRN cancellation is NOT possible if an E-Way Bill is generated corresponding to this IRN.