Reverse Charge Mechanism requires recipient self invoicing; input tax credit tied to invoice issuance year, with interest and penalties for delay. Recipients liable under the Reverse Charge Mechanism must self invoice within thirty days and maintain records; invoice level details are to be reported in Table 4B of GSTR 1 and advance payments are taxable on reverse charge basis. ECOs and suppliers using ECOs follow transitional GSTR 1/GSTR 3B reporting for specified services. Circular clarification confirms the financial year for availment of input tax credit is the year in which the recipient issues the invoice under section 31(3)(f), subject to tax payment and conditions; delayed issuance attracts interest and possible penalty.