GST vide Notification 05/2021 dated 8th March, 2021 has notified that e-invoice shall be applicable to the notified persons whose aggregate turnover exceeds Rs. 50 crores in a single financial year from 1st April, 2021.
https://www.cbic.gov.in/resources//htdocs-cbec/gst/notfctn-05-central-tax-english-2021.pdf