Aadhaar authentication requirement in GST registration can invalidate registration if authentication or alternate ID is not provided. Aadhaar authentication or proof of Aadhaar possession (or an alternate viable ID where Aadhaar is not assigned) is required for defined persons linked to a GST applicant; failure to authenticate renders the registration invalid and re-registration requires physical verification. Applications may require biometric authentication and photograph capture at notified Facilitation Centres, and mandatory Aadhaar authentication applies for revocation of cancellation, refund filings and specified export-related refunds, while classes such as non-citizens, government entities, local authorities, statutory bodies, PSUs and certain applicants are exempt.