E-invoicing under GST is triggered by aggregate turnover in any preceding financial year from 2017-18, against a threshold the Government has lowered in stages. A GIDA manufacturer, a Gorakhpur wholesaler, or an Ayodhya hotel that has crossed it must report specified invoices to the Invoice Registration Portal. A printed invoice without an IRN is not a valid tax invoice for those persons. Confirm the present threshold on the GST portal notifications; this update does not freeze a number the notification can change. See GST.
Update
E-invoicing — check the turnover threshold before the next B2B invoice
Once aggregate turnover crosses the notified GST e-invoice limit, IRP reporting is not optional.