You pay per course, and each course is under a student contribution band.
So for example, Band 2 is $8613 for 1 EFTSL (full time load). Your course in that band might be 0.125 EFTSL, so you pay $1076.625 for that course.
Your fee is also made up of your Student Amenities fee ($143.00). It should show up on the fee statement.
Now, that current liability you see in myUNSW is the upfront payment amount, which takes into account a 10% discount. If you choose not to pay upfront, after the census date, it will revert back to the full amount.
So I assume you are taking 4 band 2 courses which totals $4306.5 then add the SA fee of $143, so that is $4449.5. With a 10% upfront discount, that is $4004.55. That should be your current liability up until the census date.