Hello Bmkihara,
When it comes to writing off debt, there are several methods that one can use.
The method used depends on whether your business operates on the cash or accrual accounting basis. If you are unsure of which accounting basis your business uses, consult your tax professional or the ATO.
As there are a variety of methods for doing so,this guide for writing off bad debt may be useful in getting rid of that invoice.
I hope this helps with your inquiry.
-Ken