'Other Income' relates to business income earned under the same ABN from other sources that Airtax currently cannot pre-fill, such as Ola or Taxify. It does not include employment income (salary and wages). If you did not earn income from any such sources, you can go ahead and make this field equate to zero.
Be sure to total up this income inclusive of GST. You will see GST payable increase on your calculator once an amount has been inputted here.