A GST registration certificate issued to a 'casual taxable person' or to an 'NRI taxable person' is valid for 90 days from the date of registration, or for the period specified in the registration application, whichever occurs first. According to Section 27(1) of the CGST Act, this validity period can be extended further by a competent authority. GST registration certificates can be given to other individuals until or unless the taxpayer cancels or surrenders their registration.