Most activities carried on continuously or regularly that supply (or intend to supply) goods and services to others for payment, are taxable activities. You need carry out a taxable activity to register for GST.
GST is New Zealand’s form of indirect value-added tax. GST is a tax on the consumption of most goods and services in New Zealand. It is generally charged and accounted for at the rate of 15%. Anyone with a business turnover of NZ$60,000 or more (excluding GST) must register for and charge GST.