Extension of registration for casual and non-resident taxpayers requires electronic Form GST REG-25 filing and prescribed payment before expiry. A registered casual taxable person or non-resident taxable person seeking to extend their registration period must furnish an application in Form GST REG-25 electronically through the Common Portal, directly or via a notified facilitation centre, before the end of the registration's validity; the application will be acknowledged only on payment of the amount specified in sub-section (2) of section 19A.