GST enrolment for existing taxpayers: provisional registration must be validated online, Aadhaar-authenticated, and digitally signed. Existing taxpayers with a PAN receive provisional registration and must file an electronic enrolment application on the Common Portal supplying prescribed business, location, bank and management details and uploading specified documents. PAN, Aadhaar and other identifiers are validated online; Aadhaar consent is required for authentication. If the proper officer finds the application complete, provisional registration is confirmed and a certificate with GSTIN is issued; if incomplete or incorrect, cancellation follows after opportunity of hearing. Digital signing and authorised signatory declarations are mandated; no fee applies.