An e-invoice will be considered valid once an IRN is generated for the same. Further, it is necessary to get the IRN and QR code printed on the final invoice. Thus, when you are on the receiving side of the invoice cycle, having IRN for an invoice will be necessary to claim ITC.
Now, the e-invoice mandate, as we know, is applicable to suppliers having turnover above ₹ 500 cr. Invoices received from such suppliers need to have an IRN. While it can be anticipated that some functionality may be provided by the Government to check whether or not the taxpayer (i.e. supplier) is covered under e-invoicing, it is recommended that as a preparatory step to review your vendor master and identify the vendors who need to meet e-invoicing mandate.