If you are a student, you can use a student ID card
For housewives, you can use your husband’s NPWP and attach your family member certificate
If all the family member do not have any NPWP, the NPWP registration can be done online at the following link: https://ereg.pajak.go.id/login
Registration will take + 30 minutes. You can include proof/screenshot of the NPWP registration when you register to Duitku.
( tutorial: https://www.pajak.go.id/id/tutorial-pendaftaran-npwp-orang-pribadi-secara-online )