Issue of revised invoices for goods sold during period prior to registration :
A registered taxable person may, within one month from the date of issuance of certificate of registration and in such manner as may be prescribed, issue a revised invoice against the invoice already issued during the period beginning with the effective date of registration till the date of issuance of certificate of registration to him – section 31(3)(a) of CGST Act.
This is to enable customer to avail input tax credit during the transition period.
A taxable person is required to apply for registration within 30 days from date on which is becomes liable under GST. The aforesaid provision covers the period between date of application and date of issuance of registration certificate but not earlier period during which he was liable to pay GST.