If you use your drone for any purpose other than sport or recreation, then your drone is classified as an RPA (Remotely Piloted Aircraft) and needs to be registered by 28 January 2021. The distinction is not whether you run a drone business or earn any revenue from it, but whether you use it for any purpose (other than for sport or recreation, i.e. just for fun). If you use your drone only for sport or recreation then CASA classifies it as a model aircraft and you won't need to register at this point, though you will soon in the next phase of registration coming in March 2022.