If you are in the sharing economy (e.g ride-sharing), you may use an online platform in order to get work. Many of these platforms will charge a commission on the sale you make to the end use.
If this commission amount includes GST, it is possible that you might be able to claim this expense in your BAS. Check the invoices you get from your platform operator to confirm if there is GST or not and ensure you are entitled to claim the credit by reading through the information here.
If you are entitled to claim the GST on these commission/service fees, you can enter them in the 'rideshare fees' or 'marketing and advertising'.