Aadhaar authentication requirement: GST registration requires Aadhaar or alternate identification for individuals and entity representatives. Sub-sections (6A)-(6D) add mandatory Aadhaar authentication or proof of Aadhaar for GST registration: registered persons must authenticate or provide Aadhaar or an alternate identification; failure renders registration invalid. From a notified date, individuals and specified officials of non-individuals must authenticate or provide Aadhaar/proof or alternate identification for new registrations as prescribed; the Government may exempt classes or territories by notification. 'Aadhaar number' is defined by reference to the Aadhaar Act, 2016.