GST vide Circular No. 146/02/2021-GST dated 23rd February, 2021 has issued that QR Code shall be applicable on B2B invoices for taxpayers whose aggregate turnover exceeds Rs. 500 crores from 1st April, 2021.
https://www.cbic.gov.in/resources//htdocs-cbec/gst/Circular_Refund_146.pdf